[アルゴリズム]バックアップ-フロイド

コンセプトアレンジ

floodとshall:すべての頂点からすべての頂点への最短距離更新アルゴリズム

説明する

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;

public class baekjoon_11404 {

    static int n, m;
    static int[][] graph;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(br.readLine());
        m = Integer.parseInt(br.readLine());

        graph = new int[n + 1][n + 1];

        for (int i = 0; i < n + 1; i++) {
            Arrays.fill(graph[i], Integer.MAX_VALUE);
            graph[i][i] = 0;
        }

        for (int i = 0; i < m; i++) {
            String[] inputs = br.readLine().split(" ");
            int a = Integer.parseInt(inputs[0]);
            int b = Integer.parseInt(inputs[1]);
            int c = Integer.parseInt(inputs[2]);
            // 경로가 하나가 아닐 수 있다는 조건이 있
            graph[a][b] = Math.min(c, graph[a][b]);
        }

        floyd();

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= n; j++) {
                if (graph[i][j] == Integer.MAX_VALUE) {
                    System.out.print(0 + " ");
                } else {
                    System.out.print(graph[i][j] + " ");
                }
            }
            if (i != n) {
                System.out.println();
            }
        }
    }

    //dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j]
    private static void floyd() {
        for (int k = 1; k <= n; k++) {
            for (int i = 1; i <= n; i++) {
                for (int j = 1; j <= n; j++) {
                    if (graph[i][k] == Integer.MAX_VALUE || graph[k][j] == Integer.MAX_VALUE) {
                        continue;
                    }
                    graph[i][j] = Math.min(graph[i][j], graph[i][k] + graph[k][j]);
                }
            }
        }
    }

}