leetcode279. Perfect Squares

learn from

• DP

class Solution {
public:
    int numSquares(int n) {
        if(n<=0)return 0;
        int * dp = new int[n+1]();
        for(int i=1;i<=n;i++){
            dp[i]= INT_MAX;
            for(int j =1;j*j <=i;j++){
                int tmp = dp[i-j*j]+1;
                dp[i]=dp[i]<tmp?dp[i]:tmp;
            }
        }
        //for(int i=0;i<=n;i++)cout<< dp[i]<<' ';
        return dp[n];
    }
};

• BFS

class Solution {
public:
    int numSquares(int n) {
        if (n <= 0)return 0;
        else if(pow((int)sqrt(n),2) == n)return 1;
        vector<int> perfectSquares;//candinates
        vector<int> cntPerfectSquares(n);//count_index
        for (int i = 1; i*i <= n; i++)
        {
            perfectSquares.push_back(i*i);
            cntPerfectSquares[i*i - 1] = 1;
            
        }
        queue<int> searchQ;
        for (auto& i : perfectSquares) searchQ.push(i);
        int currCntPerfectSquares = 1;
        while (!searchQ.empty())//BFS
        {
            currCntPerfectSquares++;
            
            int searchQSize = searchQ.size();
            for (int i = 0; i < searchQSize; i++)
            {
                int tmp = searchQ.front();
                for (auto& j : perfectSquares)
                {
                    if (tmp + j == n)return currCntPerfectSquares;
                    else if ((tmp + j < n) && (cntPerfectSquares[tmp + j - 1] == 0))
                    {
                        cntPerfectSquares[tmp + j - 1] = currCntPerfectSquares;
                        searchQ.push(tmp + j);
                    }
                    else if (tmp + j > n)break;
                }
                searchQ.pop();
            }
        }
        return 0;
    }
};