Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.
The above elevation map 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. Thanks Marcos for contributing this image!
Example:
Input: [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6
class Solution {
public:
int trap(vector<int>& height) {
int size = height.size();
if (size == 0) {
return 0;
}
int ans = 0;
int left = 0, right = size - 1;
int left_iter = left + 1;
int right_iter = right - 1;
while (left <= right && left_iter <= right_iter) {
if (height[left] <= height[right]) {
left_iter = left + 1;
while (left_iter <= right_iter) {
if (height[left_iter] >= height[left]) {
left = left_iter;
break;
} else {
ans += height[left] - height[left_iter];
}
left_iter++;
}
} else {
right_iter = right - 1;
while (right_iter >= left_iter) {
if (height[right_iter] >= height[right]) {
right = right_iter;
break;
} else {
ans += height[right] - height[right_iter];
}
right_iter--;
}
}
}
return ans;
/*
cleaner one:
int trap(vector<int>& height) {
if(height.size() == 0) return 0;
int n = height.size();
int left = 0, right = n-1;
int left_max = height[left], right_max = height[right];
int area = 0;
while(left < right){
if(height[right] > height[left]){
if(left_max < height[left]){ // Difference mein paani bhar do
left_max = height[left];
}else{
area += left_max - height[left];
}
left++;
}else{
if(right_max < height[right]){
right_max = height[right];
}else{
area += right_max - height[right];
}
right--;
}
}
return area;
}
////////////////////////////////////////////////
Extra space:
int trap(vector<int>& height) {
if(height.size()<1)
return 0;
int n=height.size();
int left_max[n],right_max[n];
left_max[0]=height[0];
right_max[n-1]=height[n-1];
for(int i=1;i<n;i++){
left_max[i]=max(left_max[i-1],height[i]);
right_max[n-i-1]=max(right_max[n-i],height[n-i-1]);
}
int water=0;
for(int i=1;i<n-1;i++)
{
water+=min(left_max[i],right_max[i])-height[i];
}
return water;
}
*/
}
};
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