## 과제 : 백준 문제 풀이

목표 : 백준 문제를 풀어본다.

- [녹색 옷 입은 애가 젤다지?](https://www.acmicpc.net/problem/4485)
- [플로이드](https://www.acmicpc.net/problem/11404)
- [사이클 게임](https://www.acmicpc.net/problem/20040)
- [줄 세우기](https://www.acmicpc.net/problem/2252)

---

## 과제 : 백준 문제 풀이 모범답안

### 녹색 옷 입은 애가 젤다지?

import java.util.*;

public class Main {
    static int[] dx = {0, 1, 0, -1};
    static int[] dy = {1, 0, -1, 0};

    static class Node implements Comparable<Node> {
        int x, y, cost;

        Node(int x, int y, int cost) {
            this.x = x;
            this.y = y;
            this.cost = cost;
        }

        @Override
        public int compareTo(Node other) {
            return this.cost - other.cost;
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = 1;
        
        while (true) {
            int N = sc.nextInt();
            if (N == 0) break;

            int[][] map = new int[N][N];
            for (int i = 0; i < N; i++) {
                for (int j = 0; j < N; j++) {
                    map[i][j] = sc.nextInt();
                }
            }

            int[][] dist = new int[N][N];
            for (int[] row : dist) {
                Arrays.fill(row, Integer.MAX_VALUE);
            }
            dist[0][0] = map[0][0];

            PriorityQueue<Node> pq = new PriorityQueue<>();
            pq.add(new Node(0, 0, map[0][0]));

            while (!pq.isEmpty()) {
                Node current = pq.poll();

                for (int i = 0; i < 4; i++) {
                    int nx = current.x + dx[i];
                    int ny = current.y + dy[i];

                    if (nx >= 0 && nx < N && ny >= 0 && ny < N) {
                        int nextCost = current.cost + map[nx][ny];
                        if (nextCost < dist[nx][ny]) {
                            dist[nx][ny] = nextCost;
                            pq.add(new Node(nx, ny, nextCost));
                        }
                    }
                }
            }

            System.out.println("Problem " + t++ + ": " + dist[N-1][N-1]);
        }
    }
}

### 플로이드

import java.util.*;

public class Main {
    static final int INF = 10000000;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[][] dist = new int[n][n];

        for (int i = 0; i < n; i++) {
            Arrays.fill(dist[i], INF);
            dist[i][i] = 0;
        }

        for (int i = 0; i < m; i++) {
            int u = sc.nextInt() - 1;
            int v = sc.nextInt() - 1;
            int w = sc.nextInt();
            if (dist[u][v] > w) {
                dist[u][v] = w;
            }
        }

        for (int k = 0; k < n; k++) {
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < n; j++) {
                    if (dist[i][j] > dist[i][k] + dist[k][j]) {
                        dist[i][j] = dist[i][k] + dist[k][j];
                    }
                }
            }
        }

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                sb.append(dist[i][j] == INF ? 0 : dist[i][j]).append(" ");
            }
            sb.append("\n");
        }
        System.out.print(sb.toString());
    }
}

### 사이클 게임

import java.util.Scanner;

public class Main {
    static int[] parent;

    public static int find(int x) {
        if (parent[x] == x) {
            return x;
        }
        return parent[x] = find(parent[x]);
    }

    public static boolean union(int x, int y) {
        x = find(x);
        y = find(y);

        if (x == y) {
            return true; // 이미 같은 집합에 속해 있음 (사이클 발생)
        }
        parent[y] = x;
        return false;
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        int n = sc.nextInt();
        int m = sc.nextInt();
        
        parent = new int[n];
        for (int i = 0; i < n; i++) {
            parent[i] = i;
        }

        int result = 0;
        for (int i = 1; i <= m; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();

            if (union(a, b)) {
                result = i;
                break;
            }
        }
        System.out.println(result);
        sc.close();
    }
}

### 줄 세우기

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt(); // 학생 수
        int M = sc.nextInt(); // 비교 횟수

        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();
        int[] indegree = new int[N + 1];

        for (int i = 0; i <= N; i++) {
            adj.add(new ArrayList<>());
        }

        for (int i = 0; i < M; i++) {
            int A = sc.nextInt();
            int B = sc.nextInt();
            adj.get(A).add(B);
            indegree[B]++;
        }

        Queue<Integer> queue = new LinkedList<>();

        for (int i = 1; i <= N; i++) {
            if (indegree[i] == 0) {
                queue.offer(i);
            }
        }

        ArrayList<Integer> result = new ArrayList<>();

        while (!queue.isEmpty()) {
            int current = queue.poll();
            result.add(current);

            for (int next : adj.get(current)) {
                indegree[next]--;
                if (indegree[next] == 0) {
                    queue.offer(next);
                }
            }
        }

        for (int num : result) {
            System.out.print(num + " ");
        }

        sc.close();
    }
}