[LeetCode]Sqrt(x)

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于 2013-06-01 09:45:53 发布

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分类专栏： LeetCode

本文链接：https://blog.youkuaiyun.com/sunbaigui/article/details/8981313

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本文提供了一种使用二分查找法解决求平方根问题的C++实现方案，并通过两种不同的方法展示了如何在避免溢出的情况下找到一个整数x的平方根。

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class Solution {
//using binary search to solve sqrt(x)
//alternative method: newton method
public:
	int sqrt(int x) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		if(x <= 1) return x;
		int l = 0; 
		int r = x;
		while (l <= r)
		{
			int m = l+(r-l)/2;
			int now = x/m;//avoid overflow
			if (now < m)
				r = m-1;
			else if(now > m)
				l = m+1;
			else return m;
		}
		return r;//the small one is the answer
	}
};

second time

class Solution {
public:
    int sqrt(int x) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        long long left = 0;
        long long right = x;
        while(left <= right)
        {
            long long mid = left+(right-left)/2;
            long long square = mid*mid;//... maybe out of range
            if(square < x) left = mid+1;
            else if(square > x) right = mid-1;
            else return mid;
        }
        return (int)right;
    }
};