69. Sqrt(x)

• 二分法的妙用

 

long start = 1;
long end = x;
while(start + 1 < end){
long mid = start + (end - start)/2;

if(mid * mid <= x) start = mid;
else end = mid;
}
if(end * end <= x) return (int)end;
return (int)start;