Trapping Rain Water
Description
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.
For example, Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.
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!
Hint
Train of Thought
Code
public int trap(int[] A){
int a=0;
int b=A.length-1;
int max=0;
int leftmax=0;
int rightmax=0;
while(a<=b){
leftmax=Math.max(leftmax,A[a]);
rightmax=Math.max(rightmax,A[b]);
if(leftmax<rightmax){
max+=(leftmax-A[a]); // leftmax is smaller than rightmax, so the (leftmax-A[a]) water can be stored
a++;
}
else{
max+=(rightmax-A[b]);
b--;
}
}
return max;
}