[Coding Test] Baekjoon 알고리즘 기초 2/2 (2)

1. 600 - 그래프 1

1-1. ABCDE (13023)

import java.io.*;
import java.util.*;

class P13023_ABCDE {
    static ArrayList<Integer>[] al;
    static int N, M;
    static boolean[] visited;
    static boolean bl;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st;

        st = new StringTokenizer(br.readLine());
        N = Integer.parseInt(st.nextToken());
        M = Integer.parseInt(st.nextToken());

        visited = new boolean[N];
        al = new ArrayList[N];
        for (int i = 0; i < N; i++) {
            al[i] = new ArrayList<>();
        }

        for (int i = 0; i < M; i++) {
            st = new StringTokenizer(br.readLine());
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());

            al[a].add(b);
            al[b].add(a);
        }

        bl = false;
        for (int i = 0; i < N; i++) {
            if (!visited[i]) {
                visited[i] = true;
                dfs(i, 0);
                visited[i] = false;
            }

            if (bl) {
                break;
            }
        }

        if (bl) {
            bw.write("1\n");
        } else {
            bw.write("0\n");
        }

        bw.flush();
        bw.close();
        br.close();
    }

    public static void dfs(int num, int depth) {
        if (depth == 4) {
            bl = true;
            return;
        }

        for (int i : al[num]) {
            if (!visited[i]) {
                visited[i] = true;
                dfs(i, depth + 1);
                visited[i] = false;
            }
        }
    }
}

2. 601 - 그래프 1 (연습)

3. 602 - 그래프 1 (도전)

4. 610 - BFS

5. 620 - 트리 1

5-1. 트리 순회 (1991)

import java.io.*;
import java.util.StringTokenizer;

class Node {
    char value;
    Node left;
    Node right;

    public Node(char value) {
        this.value = value;
        this.left = null;
        this.right = null;
    }
}

public class P1991_트리순회 {
    static Node[] tree;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st;

        int N = Integer.parseInt(br.readLine());
        tree = new Node[N + 1];

        for (int i = 0; i < N; i++) {
            st = new StringTokenizer(br.readLine());
            char root = st.nextToken().charAt(0);
            char left = st.nextToken().charAt(0);
            char right = st.nextToken().charAt(0);

            if (tree[root - 'A'] == null) {
                tree[root - 'A'] = new Node(root);
            }
            if (left != '.') {
                tree[left - 'A'] = new Node(left);
                tree[root - 'A'].left = tree[left - 'A'];
            }
            if (right != '.') {
                tree[right - 'A'] = new Node(right);
                tree[root - 'A'].right = tree[right - 'A'];
            }
        }

        preorder(tree[0]);
        System.out.println();

        inorder(tree[0]);
        System.out.println();

        postorder(tree[0]);
        System.out.println();
    }

    public static void preorder(Node node) {
        if (node == null) return;
        System.out.print(node.value);
        preorder(node.left);
        preorder(node.right);
    }

    public static void inorder(Node node) {
        if (node == null) return;
        inorder(node.left);
        System.out.print(node.value);
        inorder(node.right);
    }

    public static void postorder(Node node) {
        if (node == null) return;
        postorder(node.left);
        postorder(node.right);
        System.out.print(node.value);
    }
}