Trapping Rain Water

Problem

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.

 

Example 1:

**Input:** height = [0,1,0,2,1,0,1,3,2,1,2,1]
**Output:** 6
**Explanation:** The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.

Example 2:

**Input:** height = [4,2,0,3,2,5]
**Output:** 9

 

Constraints:

• n == height.length
• 1 <= n <= 2 * 104
• 0 <= height[i] <= 105

Code

✅ Javascript

Solution

题目含义：接雨水

解题思路：

var trap = function(height) {
    let res = 0, left = 0, right = height.length - 1, maxLeft = 0, maxRight = 0;

    while(left <= right) {
        if (height[left] <= height[right]) {
            if (height[left] > maxLeft) {
                maxLeft = height[left]
            } else {
                res += maxLeft - height[left]
            }
            left += 1
        } else {
            if (height[right] >= maxRight) {
                maxRight = height[right]
            } else {
                res += maxRight - height[right]
            }
            right -= 1
        }
    }
    return res
};

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