LeetCode in TypeScript
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
function trap(height: number[]): number {
let result = 0
let left = 1
let right = height.length - 2
let leftMax = height[left - 1]
let rightMax = height[right + 1]
while (left <= right) {
if (leftMax < rightMax) {
leftMax = Math.max(leftMax, height[left])
result += leftMax - height[left]
left++
} else {
rightMax = Math.max(rightMax, height[right])
result += rightMax - height[right]
right--
}
}
return result
}
export { trap }