Largest Rectangle in Histogram

1public int largestRectangleArea(int[] heights) {
2    Stack<Integer> stack = new Stack<>();
3    int maxArea = 0;
4
5    for (int i = 0; i < heights.length; i++) {
6        while (!stack.isEmpty() && heights[i] < heights[stack.peek()]) {
7            int height = heights[stack.pop()];
8            int width = stack.isEmpty() ? i : i - stack.peek() - 1;
9            int currentArea = height * width;
10            maxArea = Math.max(maxArea, currentArea);
11        }
12
13        stack.push(i);
14    }
15
16    while (!stack.isEmpty()) {
17        int height = heights[stack.pop()];
18        int width = stack.isEmpty() ? heights.length : heights.length - stack.peek() - 1;
19        int currentArea = height * width;
20        maxArea = Math.max(maxArea, currentArea);
21    }
22
23    return maxArea;
24}