69. Sqrt(x)

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.

注意：搜索范围 [1, x]，判断条件 mid <= x / mid

time: O(x), space: O(1)

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