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84. Largest Rectangle in Histogram 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  int largestRectangleArea(vector<int>& heights) {
    int ans = 0;
    stack<int> stack;

    for (int i = 0; i <= heights.size(); ++i) {
      while (!stack.empty() &&
             (i == heights.size() || heights[stack.top()] > heights[i])) {
        const int h = heights[stack.top()];
        stack.pop();
        const int w = stack.empty() ? i : i - stack.top() - 1;
        ans = max(ans, h * w);
      }
      stack.push(i);
    }

    return ans;
  }
};

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class Solution {
  public int largestRectangleArea(int[] heights) {
    int ans = 0;
    Deque<Integer> stack = new ArrayDeque<>();

    for (int i = 0; i <= heights.length; ++i) {
      while (!stack.isEmpty() && (i == heights.length || heights[stack.peek()] > heights[i])) {
        final int h = heights[stack.pop()];
        final int w = stack.isEmpty() ? i : i - stack.peek() - 1;
        ans = Math.max(ans, h * w);
      }
      stack.push(i);
    }

    return ans;
  }
}

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class Solution:
  def largestRectangleArea(self, heights: list[int]) -> int:
    ans = 0
    stack = []

    for i in range(len(heights) + 1):
      while stack and (i == len(heights) or heights[stack[-1]] > heights[i]):
        h = heights[stack.pop()]
        w = i - stack[-1] - 1 if stack else i
        ans = max(ans, h * w)
      stack.append(i)

    return ans