279. Perfect Squares

class Solution {
public:
    int numSquares(int n)
    {
        vector<int> dp(n + 1, INT_MAX);
        dp[0] = 0;
        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j * j <= i; j++)
            {
                dp[i] = min(dp[i], dp[i - j * j] + 1);
            }
        }
        return dp[n];
    }
};

• T:
  $O(N\cdot \sqrt{N})$
• S:
  $O(N)$