Today is Saturday, I gonna review the tasks I've done this week, and finish today's leetcode's July LeetCoding Challenge with cpp.

LeetCode Review

Map Sum Pairs

too easy to review

01 Matrix

too easy to review

Beautiful Array

too easy to review

3Sum Closest

too easy to review

Convert Sorted Array to Binary Search Tree

too easy to review

Shuffle String

too easy to review

Most Visited Sector in a Circular Track

too easy to review

K-diff Pairs in an Array

too easy to review

Longest Substring Of All Vowels in Order

too easy to review

Range Sum Query - Immutable

too easy to review

July LeetCoding Challenge 31

Description

Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

Example 1:

Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.

Example 2:

Input: height = [4,2,0,3,2,5]
Output: 9

Constraints:

• n == height.length
• 0 <= n <= 3 * 10^4
• 0 <= height[i] <= 10^5

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int trap(vector<int>& height) {
    vector<int> maxRights{0};
    int len = height.size();
    for(int i = len - 1; i >= 0; --i) {
      if(height[i] >= maxRights.back()) {
        maxRights.push_back(height[i]);
      }
    }
    int maxLeft = 0;
    int answer = 0;
    for(auto h : height) {
      maxLeft = max(maxLeft, h);
      int maxRight = maxRights.back();
      int waterHeight = maxLeft > maxRight ? maxRight : maxLeft;
      answer += waterHeight > h ? (waterHeight - h) : 0;
      if(h == maxRight) {
        maxRights.pop_back();
      }
    }
    return answer;
  }
};

// Accepted
// 320/320 cases passed (4 ms)
// Your runtime beats 89.31 % of cpp submissions
// Your memory usage beats 42.07 % of cpp submissions (14.4 MB)