+ problem 493

Author: fruit-in

Problemset/0493-Reverse Pairs/README.md

@@ -0,0 +1,49 @@
+# 493. Reverse Pairs
+Given an integer array `nums`, return *the number of **reverse pairs** in the array*.
+
+A **reverse pair** is a pair `(i, j)` where:
+
+* `0 <= i < j < nums.length` and
+* `nums[i] > 2 * nums[j]`.
+
+#### Example 1:
+<pre>
+<strong>Input:</strong> nums = [1,3,2,3,1]
+<strong>Output:</strong> 2
+<strong>Explanation:</strong> The reverse pairs are:
+(1, 4) --> nums[1] = 3, nums[4] = 1, 3 > 2 * 1
+(3, 4) --> nums[3] = 3, nums[4] = 1, 3 > 2 * 1
+</pre>
+
+#### Example 2:
+<pre>
+<strong>Input:</strong> nums = [2,4,3,5,1]
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The reverse pairs are:
+(1, 4) --> nums[1] = 4, nums[4] = 1, 4 > 2 * 1
+(2, 4) --> nums[2] = 3, nums[4] = 1, 3 > 2 * 1
+(3, 4) --> nums[3] = 5, nums[4] = 1, 5 > 2 * 1
+</pre>
+
+#### Constraints:
+* <code>1 <= nums.length <= 5 * 10<sup>4</sup></code>
+* <code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code>
+
+## Solutions (Python)
+
+### 1. Solution
+```Python
+from sortedcontainers import SortedList
+
+
+class Solution:
+    def reversePairs(self, nums: List[int]) -> int:
+        sortednums = SortedList()
+        ret = 0
+
+        for num in nums:
+            ret += len(sortednums) - sortednums.bisect_right(2 * num)
+            sortednums.add(num)
+
+        return ret
+```

Problemset/0493-Reverse Pairs/README_CN.md

@@ -0,0 +1,39 @@
+# 493. 翻转对
+给定一个数组 `nums` ，如果 `i < j` 且 `nums[i] > 2*nums[j]` 我们就将 `(i, j)` 称作一个***重要翻转对***。
+
+你需要返回给定数组中的重要翻转对的数量。
+
+#### 示例 1:
+<pre>
+<strong>输入:</strong> nums = [1,3,2,3,1]
+<strong>输出:</strong> 2
+</pre>
+
+#### 示例 2:
+<pre>
+<strong>输入:</strong> nums = [2,4,3,5,1]
+<strong>输出:</strong> 3
+</pre>
+
+#### 注意:
+1. 给定数组的长度不会超过`50000`。
+2. 输入数组中的所有数字都在32位整数的表示范围内。
+
+## 题解 (Python)
+
+### 1. 题解
+```Python
+from sortedcontainers import SortedList
+
+
+class Solution:
+    def reversePairs(self, nums: List[int]) -> int:
+        sortednums = SortedList()
+        ret = 0
+
+        for num in nums:
+            ret += len(sortednums) - sortednums.bisect_right(2 * num)
+            sortednums.add(num)
+
+        return ret
+```

Problemset/0493-Reverse Pairs/Solution.py

@@ -0,0 +1,13 @@
+from sortedcontainers import SortedList
+
+
+class Solution:
+    def reversePairs(self, nums: List[int]) -> int:
+        sortednums = SortedList()
+        ret = 0
+
+        for num in nums:
+            ret += len(sortednums) - sortednums.bisect_right(2 * num)
+            sortednums.add(num)
+
+        return ret

README.md

@@ -291,6 +291,7 @@
 [483][483l]  |[Smallest Good Base][483]                                                             |![py]
 [485][485l]  |[Max Consecutive Ones][485]                                                           |![rs]
 [492][492l]  |[Construct the Rectangle][492]                                                        |![rs]
+[493][493l]  |[Reverse Pairs][493]                                                                  |![py]
 [494][494l]  |[Target Sum][494]                                                                     |![rb]  ![rs]
 [495][495l]  |[Teemo Attacking][495]                                                                |![rs]
 [496][496l]  |[Next Greater Element I][496]                                                         |![rs]
@@ -1615,6 +1616,7 @@
 [483]:Problemset/0483-Smallest%20Good%20Base/README.md#483-smallest-good-base
 [485]:Problemset/0485-Max%20Consecutive%20Ones/README.md#485-max-consecutive-ones
 [492]:Problemset/0492-Construct%20the%20Rectangle/README.md#492-construct-the-rectangle
+[493]:Problemset/0493-Reverse%20Pairs/README.md#493-reverse-pairs
 [494]:Problemset/0494-Target%20Sum/README.md#494-target-sum
 [495]:Problemset/0495-Teemo%20Attacking/README.md#495-teemo-attacking
 [496]:Problemset/0496-Next%20Greater%20Element%20I/README.md#496-next-greater-element-i
@@ -2939,6 +2941,7 @@
 [483l]:https://leetcode.com/problems/smallest-good-base/
 [485l]:https://leetcode.com/problems/max-consecutive-ones/
 [492l]:https://leetcode.com/problems/construct-the-rectangle/
+[493l]:https://leetcode.com/problems/reverse-pairs/
 [494l]:https://leetcode.com/problems/target-sum/
 [495l]:https://leetcode.com/problems/teemo-attacking/
 [496l]:https://leetcode.com/problems/next-greater-element-i/

README_CN.md

@@ -291,6 +291,7 @@
 [483][483l]  |[最小好进制][483]                                         |![py]
 [485][485l]  |[最大连续1的个数][485]                                    |![rs]
 [492][492l]  |[构造矩形][492]                                           |![rs]
+[493][493l]  |[翻转对][493]                                             |![py]
 [494][494l]  |[目标和][494]                                             |![rb]  ![rs]
 [495][495l]  |[提莫攻击][495]                                           |![rs]
 [496][496l]  |[下一个更大元素 I][496]                                   |![rs]
@@ -1615,6 +1616,7 @@
 [483]:Problemset/0483-Smallest%20Good%20Base/README_CN.md#483-最小好进制
 [485]:Problemset/0485-Max%20Consecutive%20Ones/README_CN.md#485-最大连续1的个数
 [492]:Problemset/0492-Construct%20the%20Rectangle/README_CN.md#492-构造矩形
+[493]:Problemset/0493-Reverse%20Pairs/README_CN.md#493-翻转对
 [494]:Problemset/0494-Target%20Sum/README_CN.md#494-目标和
 [495]:Problemset/0495-Teemo%20Attacking/README_CN.md#495-提莫攻击
 [496]:Problemset/0496-Next%20Greater%20Element%20I/README_CN.md#496-下一个更大元素-i
@@ -2939,6 +2941,7 @@
 [483l]:https://leetcode.cn/problems/smallest-good-base/
 [485l]:https://leetcode.cn/problems/max-consecutive-ones/
 [492l]:https://leetcode.cn/problems/construct-the-rectangle/
+[493l]:https://leetcode.cn/problems/reverse-pairs/
 [494l]:https://leetcode.cn/problems/target-sum/
 [495l]:https://leetcode.cn/problems/teemo-attacking/
 [496l]:https://leetcode.cn/problems/next-greater-element-i/