LeetCode Link: 42. Trapping Rain Water
Language: C#
Problem Statement
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.
Examples
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
Solution
public class Solution
{
public int Trap(int[] height)
{
var ml = new int[height.Length];
var mr = new int[height.Length];
var maxl = 0;
var maxr = 0;
var q = 0;
for (int i=0; i<height.Length; i++)
{
maxl = Math.Max(height[i], maxl);
maxr = Math.Max(height[height.Length - i - 1], maxr);
ml[i] = maxl;
mr[height.Length - i - 1] = maxr;
}
for (int i=0; i<height.Length; i++)
{
var hold = Math.Min(ml[i], mr[i]) - height[i];
q += hold < 0 ? 0 : hold;
}
return q;
}
}
Complexity
Time Complexity: O(N)
Space Complexity: O(N)