LeetCode 84

class Solution {
    public int largestRectangleArea(int[] h) {
        int n = h.length;
        int[] left = new int[n];
        int[] right = new int[n];
        Deque<Integer> stk = new LinkedList<>();
        for (int i = 0; i < n; i++) {
            while (!stk.isEmpty() && h[i] <= h[stk.peek()]) stk.pop();
            if (!stk.isEmpty()) left[i] = stk.peek();
            else left[i] = -1;
            stk.push(i);
        }
        stk.clear();
        for (int i = n - 1; i >= 0; i--) {
            while (!stk.isEmpty() && h[i] <= h[stk.peek()]) stk.pop();
            if (!stk.isEmpty()) right[i] = stk.peek();
            else right[i] = n;
            stk.push(i);
        }
        int res = 0;
        for (int i = 0; i < n; i++) {
            res = Math.max(res, h[i] * (right[i] - left[i] - 1));   
        }
        return res;
    }
}