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
class Solution {
public int trap(int[] height) {
int n = height.length ;
int[] leftMax = new int[n];
leftMax[0]=height[0];
for(int i=1;i<n;i++){
leftMax[i] = Math.max(leftMax[i-1],height[i]);
}
int[] rightMax = new int[n];
rightMax[n-1]=height[n-1];
for(int i=n-2;i>=0;i--){
rightMax[i] = Math.max(rightMax[i+1],height[i]);
}
int ans = 0 ;
for(int i=0;i<n;i++){
ans += Math.min(leftMax[i],rightMax[i])-height[i];
}
return ans ;
}
}
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