69. Sqrt(x) (E)

Sqrt(x) (E)

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.

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题意

手动实现 int sqrt(int x)。

思路

二分法。

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代码实现

class Solution {
    public int mySqrt(int x) {
        if (x == 0 || x == 1) {
            return x;
        }
		
        // 对于大于等于2的值x，它的平方根小于等于x/2
        int left = 1, right = x / 2;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (mid < x / mid) {
                left = mid + 1;
            } else if (mid > x / mid) {
                right = mid - 1;
            } else {
                return mid;
            }
        }
        
        return left - 1;
    }
}