【leetcode】Sqrt(x)

class Solution {
public:
int mySqrt(int x) {
unsigned long long begin=0;
unsigned long long end=(x+1)/2;
unsigned long long mid;
unsigned long long tmp;

while(begin<end)
{
mid=begin+(end-begin)/2;
tmp=mid*mid;

if(tmp==x) return mid;
else if(tmp<x) begin=mid+1;
else end=mid-1;
}

tmp=end*end;

if(tmp>x)
return end-1;
else
return end;
}
};