LeetCode-in-All
42. Trapping Rain Water
Hard
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.length1 <= n <= 2 * 1040 <= height[i] <= 105
Solution
/**
* @param {number[]} height
* @return {number}
*/
var trap = function(height) {
let l = 0
let r = height.length - 1
let res = 0
let lowerWall = 0
while (l < r) {
let lVal = height[l]
let rVal = height[r]
if (lVal < rVal) {
lowerWall = Math.max(lVal, lowerWall)
res += lowerWall - lVal
l++
} else {
lowerWall = Math.max(rVal, lowerWall)
res += lowerWall - rVal
r--
}
}
return res
};
export { trap }