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.

int mySqrt(int x) {
    if(x==0||x==1)
        return x;
    int left=1,right=x/2;
    while(left<=right)
    {
        int mid=left+(right-left)/2;
        if(mid==x/mid)
            return mid;
        if(mid<x/mid)
            left=mid+1;
        else
            right=mid-1;
    }
    return left-1;
}