Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 29

Description

Largest Rectangle in Histogram

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram.

Example 1:

Input: heights = [2,1,5,6,2,3]
Output: 10
Explanation: The above is a histogram where width of each bar is 1.
The largest rectangle is shown in the red area, which has an area = 10 units.

Example 2:

Input: heights = [2,4]
Output: 4

Constraints:

• 1 <= heights.length <= 10^5
• 0 <= heights[i] <= 10^4

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int largestRectangleArea(vector<int>& heights) {
    vector<int> st{-1};
    heights.push_back(0);
    int len = heights.size();
    int answer = 0;
    for(int i = 0; i < len; ++i) {
      while(st.back() != -1 && heights[i] < heights[st.back()]) {
        int index = st.back();
        st.pop_back();
        int h = heights[index];
        int w = i - st.back() - 1;
        answer = max(answer, h*w);
      }
      st.push_back(i);
    }
    return answer;
  }
};

// Accepted
// 96/96 cases passed (64 ms)
// Your runtime beats 99.7 % of cpp submissions
// Your memory usage beats 45.71 % of cpp submissions (64.8 MB)