题解： - 力扣（LeetCode）

class Solution {
    public int largestRectangleArea(int[] heights) {
        Stack<Integer> stack = new Stack<>();
        int maxArea = Integer.MIN_VALUE;
        for(int i = 0;i < heights.length;i++){
            int curHeight = heights[i];
            while(!stack.empty() && curHeight < heights[stack.peek()]){
                int index = stack.pop();
                int left = (stack.empty()) ? 0 : stack.peek()+1;
                int tempArea = heights[index] * (i - left);
                maxArea = Math.max(maxArea,tempArea);
            }
            stack.push(i);     
        }
        while(!stack.empty()){
                int index = stack.pop();
                int left = (stack.empty()) ? 0 : stack.peek()+1;
                int tempArea = heights[index] * (heights.length - left);
                maxArea = Math.max(maxArea,tempArea);
            }
        return maxArea;
    }
}