Time Cost

15min36s

Implementation

To find the largest rectangle area, we need to determine for each bar how far it can extend to the left and right without encountering a shorter bar. Using monotonic stacks, we can compute the Nearest Smaller to Left (NSL) and Nearest Smaller to Right (NSR) efficiently.

Code

• My Solution

  class Solution {
  public:
    int largestRectangleArea(vector<int>& heights) {
        int n = heights.size();
        vector<int> left(n), right(n);
        stack<int> st;
  
        // Nearest Smaller to Left
        for (int i = 0; i < n; i++) {
            while (!st.empty() && heights[st.top()] >= heights[i]) st.pop();
            left[i] = st.empty() ? -1 : st.top();
            st.push(i);
        }
  
        while (!st.empty()) st.pop();
  
        // Nearest Smaller to Right
        for (int i = n - 1; i >= 0; i--) {
            while (!st.empty() && heights[st.top()] >= heights[i]) st.pop();
            right[i] = st.empty() ? n : st.top();
            st.push(i);
        }
  
        int maxArea = 0;
        for (int i = 0; i < n; i++) {
            int width = right[i] - left[i] - 1;
            maxArea = max(maxArea, heights[i] * width);
        }
        return maxArea;
    }
  };