LeetCode-in-Go
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
func trap(height []int) int {
if height == nil {
return 0
}
l, r := 0, len(height)-1
maxLeft, maxRight := height[l], height[r]
res := 0
for l < r {
if maxLeft < maxRight {
l++
maxLeft = max(maxLeft, height[l])
res += maxLeft - height[l]
} else {
r--
maxRight = max(maxRight, height[r])
res += maxRight - height[r]
}
}
return res
}
func max(a, b int) int {
if a > b {
return a
}
return b
}