【算法刷题day60】Leetcode：84. 柱状图中最大的矩形

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Leetcode 84. 柱状图中最大的矩形

题目：84. 柱状图中最大的矩形
解析：代码随想录解析

解题思路

反方向接雨水。见上一篇文章

代码

class Solution {
    public int largestRectangleArea(int[] heights) {
        int[] newHeights = new int[heights.length+2];
        System.arraycopy(heights, 0, newHeights, 1, heights.length);
        int res = 0;
        Stack<Integer> stack = new Stack<>();
        stack.push(0);
        for (int i = 1; i < newHeights.length; i++) {
            if (newHeights[i] > newHeights[stack.peek()]) 
                stack.push(i);
            else if (newHeights[i] == newHeights[stack.peek()]) {
                stack.pop();
                stack.push(i);
            } else {
                while (newHeights[i] < newHeights[stack.peek()]) {
                    int mid = stack.peek();
                    stack.pop();
                    int left = stack.peek();
                    int h = newHeights[mid];
                    int w = i - left - 1;
                    res = Math.max(res, w * h);
                }
                stack.push(i);
            }
        }
        return res;
    }
}

//双指针
class Solution {
    public int largestRectangleArea(int[] heights) {
        int length = heights.length;
        int []leftHeight = new int[length];
        int []rightHeight = new int[length];
        leftHeight[0] = -1;
        for (int i = 1; i < length; i++) {
            int t = i-1;
            while (t >= 0 && heights[t] >= heights[i])
                t = leftHeight[t];
            leftHeight[i] = t;
        }
        rightHeight[length-1] = length;
        for (int i = length-2; i >= 0; i--) {
            int t = i+1;
            while (t < length && heights[t] >= heights[i])
                t = rightHeight[t];
            rightHeight[i] = t;
        }
        int res = 0;
        for (int i = 0; i < length; i++) {
            int area = (rightHeight[i] - leftHeight[i] - 1) * heights[i];
            res = Math.max(res, area);
        }
        return res;
    }
}
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总结

暂无