LeetCode problem solution --69. X square root of (C language)

Original title link:

https://leetcode-cn.com/problems/sqrtx/

topic:

Achieve int sqrt (int x) function.

Computes and returns the square root of x, where x is a non-negative integer.
Since the return type is an integer, the integer part of the result to retain only the fractional part is rounded down.

Example 1:

Input: 4 
Output: 2

Example 2:

Input: 8 
Output: 2 
Description: 8 square root is 2.82842 ..., 
     since the return type is an integer, the fractional part is rounded down.

Ideas:

Use binary search.

Because a number of the square of its own, and certainly not more than a maximum of no more than half of it, it is judged that the condition can be written ≤ x for the mid ². Since there may be written bounds case, the determination condition may be written as mid ≤ x / mid.

Code:

int mySqrt(int x){
    int l = 0, r = x;
    while(l < r)
    {
        int mid = (long long)l + r + 1 >> 1;
        if(mid <= x / mid)  l = mid;
        else r = mid - 1;
    }
    return l;
}