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.length
- 1 <= n <= 2 * 104
- 0 <= height[i] <= 105
class Solution {
public int trap(int[] height) {
int left = 0, right = height.length - 1;
int res = 0, maxleft = 0, maxright = 0;
while (left <= right) {
if (height[left] <= height[right]) {
if (height[left] >= maxleft) {
maxleft = height[left];
} else {
res += maxleft - height[left];
}
left++;
}
else {
if (height[right] >= maxright) {
maxright = height[right];
} else {
res += maxright - height[right];
}
right--;
}
}
return res;
}
}