69. Sqrt(x)(二分查找)

Implement  int sqrt(int x).

Compute and return the square root of x, where x is guaranteed to be a non-negative integer.

Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.

Example 1:

Input: 4
Output: 2

Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since 
             the decimal part is truncated, 2 is returned.

 1 class Solution {
 2     public int mySqrt(int x) {
 3         long lo = 0;
 4         long hi = x/2+1;
 5       
 6         while(lo<=hi){
 7              long mid = (hi-lo)/2+lo;
 8             if(mid*mid==x)
 9                 return (int)mid;
10             else if(mid*mid>x)
11                 hi = mid-1;
12             else
13                 lo = mid+1;
14                 
15         }
16         return (int)lo-1;
17     }
18 }