(BFS) leetcode 279. Perfect Squares

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

Example 1:

Input: n = 12
Output: 3
Explanation: 12 = 4 + 4 + 4.

Example 2:

Input: n = 13
Output: 2
Explanation: 13 = 4 + 9.
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这个题可以用BFS，不过要注意排除重复的。
C++代码：

class Solution {
public:
    int numSquares(int n) {
        if(n == )
            return ;
        queue<pair<int,int> > q;
        q.push(make_pair(n,));
        vector<bool> vis(n+,false);  //用这个来避免把重复的数加进队列。
        vis[n] = true;
        while(!q.empty()){
            int num = q.front().first;
            int s = q.front().second;
            q.pop();
            if(num == )
                return ;
            for(int i = ; num - i*i >= ; i++){
                int ans = num - i*i;
                if(ans == )
                    return s;
                if(!vis[ans]){
                    q.push(make_pair(ans,s+));
                    vis[ans] = true;
                }
            }
        }
        return ;
    }
};