[LeetCode] 84. Largest Rectangle in Histogram

https://leetcode.com/problems/largest-rectangle-in-histogram/

public class Solution {
    public int largestRectangleArea(int[] heights) {
        int result = 0;
        Stack<Integer> stack = new Stack<>();
        for (int i = 0; i < heights.length; i++) {
            while (!stack.isEmpty() && heights[stack.peek()] >= heights[i]) {
                int tmp = stack.pop();
                int height = heights[tmp];
                int width = stack.isEmpty() ? i : i - stack.peek() - 1;
                result = Math.max(result, height * width);
            }
            stack.push(i);
        }
        
        // process the numbers left in stack
        while (!stack.isEmpty() && heights[stack.peek()] >= 0) {
            int tmp = stack.pop();
            int height = heights[tmp];
            int width = stack.isEmpty() ? heights.length : heights.length - stack.peek() - 1;
            result = Math.max(result, height * width);
        }
        return result;
    }
}