69 Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

x is guaranteed to be a non-negative integer.

Example 1:

Input: 4
Output: 2
Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since we want to return an integer, the decimal part will be truncated.

class Solution {
    public int mySqrt(int x) {
      long low = 0;  
        long high = x/2+1;//平方根的值按规律发现不会大于它的中值+1。这样每个查找就少了一次  
        long tmp;  
        long mid = 1;  
        while (low <= high)  
        {  
            mid = (low + high) / 2;  
            tmp = mid * mid;  
            if (tmp == x)  
                return (int)mid;  
            else if (tmp > x)  
                high = mid - 1;  
            else if (tmp < x)  
                low = mid + 1;  
        }  
        return (int)high;  
    }
}

二分法的应用