Perfect squares for leetcode topic analysis

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.

Dynamic programming , Solve the optimization problem , Bottom up .

    public int numSquares(int n) {
        int[] dp = new int[n + 1];
        Arrays.fill(dp, Integer.MAX_VALUE);
        //  Set all squares 1
        for (int i = 0; i * i <= n; i++) {
            dp[i * i] = 1;
        }
        for (int a = 1; a <= n; a++) {
            for (int b = 1; a + b * b <= n; b++) {
                //  Take the smaller value ,a + b * b It can also be a square number 
                dp[a + b * b] = Math.min(dp[a] + 1, dp[a + b * b]);
            }
        }
        return dp[n];
    }