java刷题--42接雨水

Posted 2021-08-20 Anrys

java刷题--42接雨水

• 题目
• 代码
• 结果

题目

代码

暴力法

class Solution {
    public int trap(int[] height) {
        int ans = 0;
        int size = height.length;
        for (int i = 1; i < size - 1; i++) {
            int max_left = 0, max_right = 0;
            for (int j = i; j >= 0; j--) { //Search the left part for max bar size
                max_left = Math.max(max_left, height[j]);
            }
            for (int j = i; j < size; j++) { //Search the right part for max bar size
                max_right = Math.max(max_right, height[j]);
            }
            ans += Math.min(max_left, max_right) - height[i];
        }
        return ans;
    }
}

动态规划–道理都是一样的

class Solution {
    public int trap(int[] height) {
        int n = height.length;
        if (n == 0) return 0 ;
        int[] leftMax = new int[n];
        leftMax[0] = height[0];
        for (int i = 1; i < n; i++) {
            leftMax[i] = Math.max(leftMax[i - 1], height[i]);
        }

        int[] rightMax = new int[n];
        rightMax[n - 1] = height[n - 1];
        for (int i = n - 2; i >= 0; --i) {
            rightMax[i] = Math.max(rightMax[i + 1], height[i]);
        }

        int ans = 0;
        for (int i = 0; i < n; ++i) {
            ans += Math.min(leftMax[i], rightMax[i]) - height[i];
        }
        return ans;
    }
}

结果