LeetCode OJ：Sqrt(x)（平方根）

 1 class Solution {
 2 public:
 3     int mySqrt(int x) {
 4         if(x == 0 || x == 1) return x;
 5         int beg = 1;
 6         int end = x;
 7         long mid = 0;   //这里用long，否则会溢出
 8         while(beg <= end){
 9             mid = beg + (end - beg)/2;
10             if(mid * mid < x){
11                 beg = mid + 1;
12             }else if(mid * mid > x){
13                 end = mid - 1;
14             }else{
15                 return mid;
16             }
17         }
18         return end;
19     }
20 };