279.完全平方数 (Medium)*

class Solution {
public:
    int numSquares(int n) {
        vector<int> dp(n + 1);
        for(int i = 1; i <= n; i++) {
            dp[i] = i;
            for(int j = 1; j * j <= i; j++) {
                dp[i] = min(dp[i], dp[i - j * j] + 1);
            }
        }
        return dp[n];
    }
};

class Solution {
public:
    int numSquares(int n) {
        vector<bool> visited(n + 1, false);
        queue<int> bfs;
        bfs.push(n);
        int steps = 0;
        while(!bfs.empty()) {
            int len = bfs.size();
            steps++;
            for(int i = 0; i < len; i++) {
                int cur = bfs.front();
                bfs.pop();
                for(int j = 1; j * j <= cur; j++) {
                    int tmp = cur - j * j;
                    if(tmp == 0) {
                        return steps;
                    }
                    if(!visited[tmp]) {
                        bfs.push(tmp);
                        visited[tmp] = true;
                    }
                }
            }
        }
        return -1;
    }
};