381 runtime error

Author: aQua

Algorithms/0381.insert-delete-getrandom-o1-duplicates-allowed/README.md

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+# [381. Insert Delete GetRandom O(1) - Duplicates allowed](https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed/)
+
+## 题目
+Design a data structure that supports all following operations in average O(1) time.
+Note: Duplicate elements are allowed.
+
+1. insert(val): Inserts an item val to the collection.
+1. remove(val): Removes an item val from the collection if present.
+1. getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.
+
+
+
+Example:
+```
+// Init an empty collection.
+RandomizedCollection collection = new RandomizedCollection();
+
+// Inserts 1 to the collection. Returns true as the collection did not contain 1.
+collection.insert(1);
+
+// Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1].
+collection.insert(1);
+
+// Inserts 2 to the collection, returns true. Collection now contains [1,1,2].
+collection.insert(2);
+
+// getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.
+collection.getRandom();
+
+// Removes 1 from the collection, returns true. Collection now contains [1,2].
+collection.remove(1);
+
+// getRandom should return 1 and 2 both equally likely.
+collection.getRandom();
+```
+## 解题思路
+
+见程序注释

Algorithms/0381.insert-delete-getrandom-o1-duplicates-allowed/insert-delete-getrandom-o1-duplicates-allowed.go

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+package Problem0381
+
+import "math/rand"
+
+// RandomizedCollection 是一个随机获取的集合
+type RandomizedCollection struct {
+	a   []int
+	idx map[int][]int // idx 的 v 是 k 在 a 中的位置。
+}
+
+// Constructor returns RandomizedSet
+/** Initialize your data structure here. */
+func Constructor() RandomizedCollection {
+	return RandomizedCollection{
+		a:   []int{},
+		idx: make(map[int][]int),
+	}
+}
+
+// Insert 插入数据
+/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
+func (r *RandomizedCollection) Insert(val int) bool {
+	res := false
+	if _, ok := r.idx[val]; !ok {
+		res = true
+	}
+	r.a = append(r.a, val)
+	r.idx[val] = append(r.idx[val], len(r.a)-1)
+	return res
+}
+
+// Remove 删除数据
+/** Removes a value from the collection. Returns true if the collection contained the specified element. */
+func (r *RandomizedCollection) Remove(val int) bool {
+	if _, ok := r.idx[val]; !ok {
+		return false
+	}
+
+	last := r.a[len(r.a)-1]
+	lenOfLast := len(r.idx[last])
+	lenOfVal := len(r.idx[val])
+	// 把 a 的最后一个数，放入最后一个 val 的位置
+	r.a[r.idx[val][lenOfVal-1]] = last
+	r.idx[last][lenOfLast-1] = r.idx[val][lenOfVal-1]
+
+	// 删除最后一个数
+	r.a = r.a[:len(r.a)-1]
+	// 在 r.idx 中删除 val 的记录
+	if lenOfVal == 1 {
+		delete(r.idx, val)
+	} else {
+		r.idx[val] = r.idx[val][:lenOfVal-1]
+	}
+
+	return true
+}
+
+// GetRandom 获取随机数据
+/** Get a random element from the collection. */
+func (r *RandomizedCollection) GetRandom() int {
+	return r.a[rand.Intn(len(r.a))]
+}

Algorithms/0381.insert-delete-getrandom-o1-duplicates-allowed/insert-delete-getrandom-o1-duplicates-allowed_test.go

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+package Problem0381
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Problem0381(t *testing.T) {
+	ast := assert.New(t)
+
+	rs := Constructor()
+
+	ast.True(rs.Insert(1), "插入1")
+
+	ast.False(rs.Remove(2), "删除2")
+
+	ast.True(rs.Insert(2), "插入2")
+
+	ast.Contains([]int{1, 2}, rs.GetRandom(), "返回1或2")
+
+	ast.True(rs.Remove(1), "删除1")
+
+	ast.False(rs.Insert(2), "再一次插入2")
+
+	ast.Equal(2, rs.GetRandom(), "从只有2的集合中随机取出2")
+
+	length := 100
+	result := make([]int, length)
+	for i := 0; i < 100; i++ {
+		rs.Insert(i)
+		result[i] = i
+	}
+	ast.Contains(result, rs.GetRandom(), "随机获取0~100之间的数")
+}