279. Perfect Squares

```java
class Solution {
    public int numSquares(int n) {
        Integer[] memo = new Integer[n+1];        
        return dfs(n, memo);
    }
    private int dfs(int n, Integer[] memo) {
        if (n == 0) {
            return 0;
        }
        if (memo[n] != null) {
            return memo[n];
        }
        int count = Integer.MAX_VALUE;
        for (int i = 1; i*i <= n; i++) {
            count = Math.min(count, dfs(n - i*i, memo) + 1);
        }
        return memo[n] = count;
    }
}
```

✅ Java | Recursion ➜ Memoization ➜ DP ➜ 3 Square Theorem (Explained) - Perfect Squares - LeetCodeLeetCode