[leetcode]633. Sum of Square Numbers

题目链接：https://leetcode.com/problems/sum-of-square-numbers/#/description

Given a non-negative integer c, your task is to decide whether there're two integers a and b such that a2 + b2 = c.

Example 1:

Input: 5Output: TrueExplanation: 1 * 1 + 2 * 2 = 5

Example 2:

Input: 3Output: False

class Solution {public:    bool judgeSquareSum(int c) {        for(long a=0;a*a<=c;a++)        {            int b=c-(int)(a*a);            if(binary_search(0,b,b))                return true;        }        return false;    }        bool binary_search(long s,long e,int n)    {        if(s>e)            return false;        long mid=s+(e-s)/2;        if(mid*mid==n)            return true;        else if(mid*mid>n)            return binary_search(s,mid-1,n);        else if(mid*mid<n)            return binary_search(mid+1,e,n);        return false;    }};

class Solution {public:    bool judgeSquareSum(int c) {        for(long long a=0;a*a<=c;a++)        {            int b=c-(long long)(a*a);            if(binary_search(0,b,b))                return true;        }        return false;    }private:    bool binary_search(long long left,long long right,long long n)    {        while(left<=right)        {            long long mid=left+(right-left)/2;            if(mid*mid==n)                return true;            else if(mid*mid>n)                right=mid-1;            else                left=mid+1;        }        return false;    }};