코테에서 자주 쓰이는 알고리즘 기본형 With GPT
DFS
import java.util.*;
public class DFS {
public static void dfs(int v, boolean[] visited, List<List<Integer>> graph) {
visited[v] = true;
System.out.print(v + " ");
for (int i : graph.get(v)) {
if (!visited[i]) {
dfs(i, visited, graph);
}
}
}
public static void main(String[] args) {
List<List<Integer>> graph = new ArrayList<>();
for (int i = 0; i < 5; i++) {
graph.add(new ArrayList<>());
}
graph.get(0).add(1);
graph.get(0).add(2);
graph.get(1).add(0);
graph.get(1).add(3);
graph.get(2).add(0);
graph.get(2).add(4);
graph.get(3).add(1);
graph.get(4).add(2);
boolean[] visited = new boolean[5];
dfs(0, visited, graph);
}
}
BFS
import java.util.*;
public class BFS {
public static void bfs(int start, List<List<Integer>> graph) {
boolean[] visited = new boolean[graph.size()];
Queue<Integer> queue = new LinkedList<>();
queue.add(start);
visited[start] = true;
while (!queue.isEmpty()) {
int v = queue.poll();
System.out.print(v + " ");
for (int i : graph.get(v)) {
if (!visited[i]) {
visited[i] = true;
queue.add(i);
}
}
}
}
public static void main(String[] args) {
List<List<Integer>> graph = new ArrayList<>();
for (int i = 0; i < 5; i++) {
graph.add(new ArrayList<>());
}
graph.get(0).add(1);
graph.get(0).add(2);
graph.get(1).add(0);
graph.get(1).add(3);
graph.get(2).add(0);
graph.get(2).add(4);
graph.get(3).add(1);
graph.get(4).add(2);
bfs(0, graph);
}
}
다익스트라
import java.util.*;
public class Dijkstra {
static class Node implements Comparable<Node> {
int vertex, weight;
Node(int v, int w) {
this.vertex = v;
this.weight = w;
}
public int compareTo(Node other) {
return this.weight - other.weight;
}
}
public static void dijkstra(int start, List<List<Node>> graph) {
int n = graph.size();
int[] dist = new int[n];
Arrays.fill(dist, Integer.MAX_VALUE);
dist[start] = 0;
PriorityQueue<Node> pq = new PriorityQueue<>();
pq.add(new Node(start, 0));
while (!pq.isEmpty()) {
Node node = pq.poll();
int v = node.vertex;
int w = node.weight;
for (Node neighbor : graph.get(v)) {
int newDist = w + neighbor.weight;
if (newDist < dist[neighbor.vertex]) {
dist[neighbor.vertex] = newDist;
pq.add(new Node(neighbor.vertex, newDist));
}
}
}
System.out.println(Arrays.toString(dist));
}
public static void main(String[] args) {
List<List<Node>> graph = new ArrayList<>();
for (int i = 0; i < 5; i++) {
graph.add(new ArrayList<>());
}
graph.get(0).add(new Node(1, 10));
graph.get(0).add(new Node(2, 3));
graph.get(1).add(new Node(2, 1));
graph.get(1).add(new Node(3, 2));
graph.get(2).add(new Node(3, 8));
graph.get(3).add(new Node(4, 7));
dijkstra(0, graph);
}
}
플로이드워셜
import java.util.*;
public class FloydWarshall {
public static void floydWarshall(int[][] graph) {
int n = graph.length;
int[][] dist = new int[n][n];
for (int i = 0; i < n; i++) {
System.arraycopy(graph[i], 0, dist[i], 0, n);
}
for (int k = 0; k < n; k++) {
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (dist[i][k] + dist[k][j] < dist[i][j]) {
dist[i][j] = dist[i][k] + dist[k][j];
}
}
}
}
for (int[] row : dist) {
System.out.println(Arrays.toString(row));
}
}
public static void main(String[] args) {
int INF = 99999;
int[][] graph = {
{0, 3, INF, 5},
{2, 0, INF, 4},
{INF, 1, 0, INF},
{INF, INF, 2, 0}
};
floydWarshall(graph);
}
}
벨만포드
import java.util.*;
public class BellmanFord {
public static void bellmanFord(int[][] edges, int V, int start) {
int[] dist = new int[V];
Arrays.fill(dist, Integer.MAX_VALUE);
dist[start] = 0;
for (int i = 0; i < V - 1; i++) {
for (int[] edge : edges) {
int u = edge[0], v = edge[1], w = edge[2];
if (dist[u] != Integer.MAX_VALUE && dist[u] + w < dist[v]) {
dist[v] = dist[u] + w;
}
}
}
for (int[] edge : edges) {
int u = edge[0], v = edge[1], w = edge[2];
if (dist[u] != Integer.MAX_VALUE && dist[u] + w < dist[v]) {
System.out.println("Negative weight cycle detected");
return;
}
}
System.out.println(Arrays.toString(dist));
}
public static void main(String[] args) {
int V = 5;
int[][] edges = {
{0, 1, -1}, {0, 2, 4},
{1, 2, 3}, {1, 3, 2}, {1, 4, 2},
{3, 2, 5}, {3, 1, 1}, {4, 3, -3}
};
bellmanFord(edges, V, 0);
}
}
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