279. Perfect Squares

class Solution {
public:
    int numSquares(int n) {
        vector<int> c;
        for (int i = 1; i*i <=n; i++)
            c.push_back(i*i);
        queue<int> q;
        q.push(0);
        int lv = 0;
        while (!q.empty()) {
            int qs = q.size();
            lv++;
            while (qs-- > 0) {
                int cur = q.front();
                q.pop();
                for (int i : c) {
                    if (cur + i == n) {
                        return lv;
                    }
                    else if (cur + i > n)
                        break;
                    else
                        q.push(cur+i);
                }
            }
        }
        return lv;
    }
};