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solve problem Sort Characters By Frequency
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‎README.md

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|394|[Decode String](https://leetcode-cn.com/problems/decode-string/description/)|[java/py/js](./algorithms/DecodeString)|Medium|
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|938|[Range Sum Of Bst](https://leetcode-cn.com/problems/range-sum-of-bst/description/)|[java/py/js](./algorithms/RangeSumOfBst)|Medium|
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|71|[Simplify Path](https://leetcode-cn.com/problems/simplify-path/description/)|[java/py/js](./algorithms/SimplifyPath)|Medium|
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|451|[Sort Characters By Frequency](https://leetcode-cn.com/problems/sort-characters-by-frequency/description/)|[java/py/js](./SortCharactersByFrequency)|Medium|
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# Database
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|#|Title|Solution|Difficulty|

‎algorithms/SortCharactersByFrequency/README.md

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# Sort Characters By Frequency
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We can solve this problem by heap

‎algorithms/SortCharactersByFrequency/Solution.java

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class Solution {
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class MaxHeap {
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class Node {
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Object item;
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int priority;
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Node(Object item, int priority) {
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this.item = item;
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this.priority = priority;
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}
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}
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ArrayList<Node> heap;
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MaxHeap() {
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this.heap = new ArrayList<Node>();;
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}
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void push(Object item, int priority) {
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heap.add(new Node(item, priority));
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int pos = heap.size() - 1;
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int pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2;
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while (pPos >= 0 && priority > heap.get(pPos).priority) {
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Node temp = heap.get(pPos);
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heap.set(pPos, heap.get(pos));
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heap.set(pos, temp);
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pos = pPos;
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pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2;
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}
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}
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int size() {
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return heap.size();
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}
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Object pop() {
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int size = heap.size();
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if (size == 0)
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throw new ArrayIndexOutOfBoundsException("pop from empty list");
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else if (size == 1)
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return heap.remove(0).item;
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Object item = heap.get(0).item;
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int pos = 0;
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int maxChildPos = pos * 2 + 2;
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heap.set(0, heap.remove(size - 1));
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if (maxChildPos < size - 1)
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maxChildPos = heap.get(maxChildPos).priority > heap.get(maxChildPos - 1).priority ? maxChildPos : maxChildPos - 1;
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos;
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while (maxChildPos < size - 1 && heap.get(pos).priority < heap.get(maxChildPos).priority) {
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Node temp = heap.get(maxChildPos);
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heap.set(maxChildPos, heap.get(pos));
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heap.set(pos, temp);
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pos = maxChildPos;
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maxChildPos = pos * 2 + 2;
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if (maxChildPos < size - 1)
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maxChildPos = heap.get(maxChildPos).priority > heap.get(maxChildPos - 1).priority ? maxChildPos : maxChildPos - 1;
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos;
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}
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return item;
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}
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}
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public String frequencySort(String s) {
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Map<Character, Integer> charMap = new HashMap<Character, Integer>();
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for (char c : s.toCharArray()) {
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if (charMap.get(c) == null)
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charMap.put(c, 1);
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else
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charMap.put(c, charMap.get(c) + 1);
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}
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MaxHeap maxHeap = new MaxHeap();
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for (char c : charMap.keySet())
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maxHeap.push(c, charMap.get(c));
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StringBuilder sb = new StringBuilder();
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while (maxHeap.size() > 0) {
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char c = (char) maxHeap.pop();
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for (int i = 0; i < charMap.get(c); i++)
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sb.append(String.valueOf(c));
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}
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return sb.toString();
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}
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}

‎algorithms/SortCharactersByFrequency/solution.js

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/**
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* @param {string} s
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* @return {string}
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*/
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var frequencySort = function(s) {
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let charMap = {}
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s.split('').forEach(c => {
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if (charMap[c] == undefined)
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charMap[c] = 1
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else
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charMap[c]++
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})
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let maxHeap = new MaxHeap()
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Object.keys(charMap).forEach(key => {
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maxHeap.push(key, charMap[key])
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})
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let res = ''
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while (maxHeap.size() > 0) {
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let key = maxHeap.pop()
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for (let i = 0; i < charMap[key]; i++)
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res += key
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}
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return res
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};
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function MaxHeap() {
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this.heap = []
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};
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MaxHeap.prototype.push = function(item, priority) {
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this.heap.push({item, priority})
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let pos = this.heap.length - 1,
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pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2
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while (pPos >= 0 && priority > this.heap[pPos].priority) {
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let temp = this.heap[pos]
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this.heap[pos] = this.heap[pPos]
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this.heap[pPos] = temp
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pos = pPos
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pPos = (pos % 2 == 0 ? pos - 2 : pos - 1) / 2
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}
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};
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MaxHeap.prototype.size = function() {
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return this.heap.length
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};
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MaxHeap.prototype.pop = function() {
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let size = this.size()
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if (size == 0)
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throw new Error('pop form empty list')
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else if (size == 1)
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return this.heap.pop().item
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let item = this.heap[0].item,
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pos = 0,
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maxChildPos = pos * 2 + 2
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this.heap[0] = this.heap.pop()
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if (maxChildPos < size - 1)
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maxChildPos = this.heap[maxChildPos].priority > this.heap[maxChildPos - 1].priority ? maxChildPos : maxChildPos - 1
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos
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while (maxChildPos < size - 1 && this.heap[pos].priority < this.heap[maxChildPos].priority) {
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let temp = this.heap[maxChildPos]
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this.heap[maxChildPos] = this.heap[pos]
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this.heap[pos] = temp
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pos = maxChildPos
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maxChildPos = pos * 2 + 2
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if (maxChildPos < size - 1)
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maxChildPos = this.heap[maxChildPos].priority > this.heap[maxChildPos - 1].priority ? maxChildPos : maxChildPos - 1
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else
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maxChildPos = maxChildPos - 1 < size - 1 ? maxChildPos - 1 : pos
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}
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return item
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};

‎algorithms/SortCharactersByFrequency/solution.py

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class Solution(object):
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class MaxHeap(object):
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'''
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simple max heap for this solution
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'''
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def __init__(self):
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self.heap = []
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def push(self, item, priority):
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self.heap.append({ 'item': item, 'priority': priority })
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pos = self.size() - 1
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p_pos = (pos - 2 if pos % 2 == 0 else pos - 1) / 2
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while p_pos >= 0 and priority > self.heap[p_pos]['priority']:
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self.heap[pos], self.heap[p_pos] = self.heap[p_pos], self.heap[pos]
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pos = p_pos
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p_pos = (pos - 2 if pos % 2 == 0 else pos - 1) / 2
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def size(self):
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return len(self.heap)
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def pop(self):
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size = self.size()
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if size == 0:
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raise IndexError('pop form empty list')
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elif size == 1:
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return self.heap.pop()['item']
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item = self.heap[0]['item']
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self.heap[0] = self.heap.pop()
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pos = 0
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max_child_pos = pos * 2 + 2
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if max_child_pos < size - 1:
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max_child_pos = max_child_pos if self.heap[max_child_pos]['priority'] > self.heap[max_child_pos - 1]['priority'] else max_child_pos - 1
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else:
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max_child_pos = max_child_pos - 1 if max_child_pos - 1 < size - 1 else pos
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while max_child_pos < size - 1 and self.heap[pos]['priority'] < self.heap[max_child_pos]['priority']:
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self.heap[pos], self.heap[max_child_pos] = self.heap[max_child_pos], self.heap[pos]
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pos = max_child_pos
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max_child_pos = pos * 2 + 2
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if max_child_pos < size - 1:
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max_child_pos = max_child_pos if self.heap[max_child_pos]['priority'] > self.heap[max_child_pos - 1]['priority'] else max_child_pos - 1
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else:
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max_child_pos = max_child_pos - 1 if max_child_pos - 1 < size - 1 else pos
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return item
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def frequencySort(self, s):
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"""
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:type s: str
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:rtype: str
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"""
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char_map = {}
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for c in s:
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if not char_map.get(c):
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char_map[c] = 1
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else:
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char_map[c] += 1
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max_heap = Solution.MaxHeap()
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for key, value in char_map.items():
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max_heap.push(key, value)
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res = ''
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while max_heap.size() > 0:
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c = max_heap.pop()
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res += char_map[c] * c
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return res

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