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!
双指针，需要把情况考虑全。
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class
Solution {
public:
int
trap(int
A[], int
n) {
int
result = 0;
int
l = 0,r = n-1;
while(A[l]==0)l++;
while(A[r]==0)r--;
int
h = 0;
h = min(A[l],A[r]);
while(l < r)
{
if(A[l] <= h)
{
result += h - A[l];
l++;
}
else
if(A[r] < h)
{
result += h - A[r];
r--;
}
else
if(A[l] > h && A[r] == h)
{
r--;
}
else
if(A[r] > h && A[l] == h)
{
l++;
}
else
if(A[l]>h &&A[r]>h)
{
h = min(A[l],A[r]);
}
}
return
result;
}
}; |