Leetcode 279. Perfect Squares

279. Perfect Squares

アプローチ 1

DP

package com.leetcode.midium;

import java.util.Arrays;

public class PerfectSquares279 {
    public static void main(String[] args) {

    }

    public static 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++) {
            for (int j = 1; j * j <= i; j++) {
                dp[i] = Math.min(dp[i], dp[i - j * j] + 1);
            }
        }
        return dp[n];
    }
}

アプローチ 2

BFS

class Solution {
    public int numSquares(int n) {
        Queue<Integer> queue = new LinkedList<Integer>();
        Set<Integer> alreadyAddedSquareNumbers = new HashSet<Integer>();
        int level = 0;
        queue.add(0);
        
        while(!queue.isEmpty()){
            level++;
            int previousLevel = queue.size();
            for(int index = 0; index < previousLevel; index++){
                int base = queue.poll();
                
                for(int square = 1; square * square <= n - base; square++){
                    int sumOfSquares = base + square * square;
                    if(alreadyAddedSquareNumbers.contains(base + square * square) || sumOfSquares > n){
                        continue;
                    }
                    if(sumOfSquares == n) {
                        return level;
                    } else {
                        queue.add(sumOfSquares);
                        alreadyAddedSquareNumbers.add(sumOfSquares);
                    }
                }
            }
        }
        return -1;
    }
}