279. Perfect Squares

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題目敘述

Given an integer n, return the least number of perfect square numbers that sum to n.

A perfect square is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, 1, 4, 9, and 16 are perfect squares while 3 and 11 are not.

Example 1

Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4.

Example 2

Input: n = 13 Output: 2 Explanation: 13 = 4 + 9.

解題思路

Solution

import java.util.Arrays;

class Solution {
    public int numSquares(int n) {
        int[] dp = new int[n + 1];
        Arrays.fill(dp, Integer.MAX_VALUE);
        
        dp[0] = 0;
        
        for (int i = 1; i <= n; i++) {
            int min_val = Integer.MAX_VALUE;
            for (int j = 1; j * j <= i; j++) {
                min_val = Math.min(min_val, dp[i - j * j] + 1);
            }
            dp[i] = min_val;
        }
        
        return dp[n];
    }
}