[Leetcode] Sqrt(x)

Sqrt(x) 题解

题目来源：https://leetcode.com/problems/sqrtx/description/

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Description

Implement int sqrt(int x).

Compute and return the square root of x.

x is guaranteed to be a non-negative integer.

Example

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.

Solution

class Solution {
public:
    int mySqrt(int x) {
        if (x == 0)
            return 0;
        if (x <= 3)
            return 1;
        int low = 2;
        int high = x / 2;
        while (low <= high) {
            int mid = (low + high) / 2;
            if (mid > x / mid) {
                high = mid;
            } else if (mid + 1 <= x / (mid + 1)) {
                low = mid;
            } else {
                return mid;
            }
        }
    }
};

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解题描述

这道题是要实现一个开平方根的函数，且返回值是平方根进行截断后的整数部分，这里考虑的做法是二分查找，针对输入数字大于4的情况，下界定为2，上界定位输入数的一半。