From a6e20d3f65eb9d912f38dc9fb2a27b85e79f2f7a Mon Sep 17 00:00:00 2001
From: oncsr <khj20006@naver.com>
Date: Sun, 21 Dec 2025 21:15:36 +0900
Subject: [PATCH] =?UTF-8?q?[20251221]=20BOJ=20/=20D5=20/=20Graph=20Constru?=
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 create mode 100644 khj20006/202512/21 BOJ D5 Graph Construction.md

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+```java
+import java.util.*;
+import java.io.*;
+
+class DisjointSet {
+    int[] root, cnt;
+    Stack<int[]> works;
+    DisjointSet(int size) {
+        root = new int[size];
+        cnt = new int[size];
+        for(int i=0;i<size;i++) {
+            root[i] = i;
+            cnt[i] = 1;
+        }
+        works = new Stack<>();
+    }
+
+    int find(int x) { return x == root[x] ? x : find(root[x]); }
+
+    void union(int a, int b) {
+        int x = find(a), y = find(b);
+        if(x == y) {
+            works.push(new int[]{-1,-1,-1});
+            return;
+        }
+        if(cnt[x] > cnt[y]) {
+            int temp = x;
+            x = y;
+            y = temp;
+        }
+        works.push(new int[]{x, y, cnt[x]});
+        cnt[y] += cnt[x];
+        root[x] = y;
+    }
+
+    void rollback() {
+        if(!works.empty()) {
+            int[] info = works.pop();
+            int x = info[0], y = info[1], c = info[2];
+            if(x != -1) {
+                root[x] = x;
+                cnt[y] -= c;
+            }
+        }
+    }
+}
+
+public class Main {
+
+    static BufferedReader br;
+    static BufferedWriter bw;
+    static StringTokenizer st;
+
+    static int N, K;
+    static List<int[]>[] edges;
+    static int[][] finds;
+    static Map<String, Integer> edgeTime;
+    static DisjointSet ds;
+
+    public static void main(String[] args) throws Exception {
+        bw = new BufferedWriter(new OutputStreamWriter(System.out));
+
+        input();
+        solve();
+
+        bw.close();
+    }
+
+    public static void input() throws Exception {
+        br = new BufferedReader(new InputStreamReader(System.in));
+
+        st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        K = Integer.parseInt(st.nextToken());
+        edges = new List[4*K];
+        finds = new int[K+1][2];
+        for(int i=1;i<=K;i++) finds[i] = new int[]{-1,-1};
+        for(int i=1;i<4*K;i++) edges[i] = new ArrayList<>();
+        edgeTime = new TreeMap<>();
+        for(int i=1;i<=K;i++) {
+            st = new StringTokenizer(br.readLine());
+            int op = Integer.parseInt(st.nextToken());
+            int a = Integer.parseInt(st.nextToken());
+            int b = Integer.parseInt(st.nextToken());
+            if(op == 3) finds[i] = new int[]{a,b};
+            else {
+                if(op == 1) edgeTime.put(a + " " + b, i);
+                else {
+                    int start = edgeTime.get(a + " " + b);
+                    edgeTime.remove(a + " " + b);
+                    update(1,K,start,i,a,b,1);
+                }
+            }
+        }
+        for(String key : edgeTime.keySet()) {
+            int start = edgeTime.get(key);
+            String[] sp = key.split(" ");
+            int a = Integer.parseInt(sp[0]);
+            int b = Integer.parseInt(sp[1]);
+            update(1,K,start,K,a,b,1);
+        }
+
+        br.close();
+    }
+
+    public static void update(int s, int e, int l, int r, int a, int b, int n) {
+        if(l>r || l>e || r<s) return;
+        if(l<=s && e<=r) {
+            edges[n].add(new int[]{a, b});
+            return;
+        }
+        int m = (s+e)>>1;
+        update(s,m,l,r,a,b,n*2);
+        update(m+1,e,l,r,a,b,n*2+1);
+    }
+
+    public static void solve() throws Exception {
+        ds = new DisjointSet(N);
+        dnc(1,K,1);
+    }
+
+    public static void dnc(int s, int e, int n) throws Exception {
+        for(int[] edge : edges[n]) {
+            int a = edge[0], b = edge[1];
+            ds.union(a,b);
+        }
+
+        if(s == e) {
+            if(finds[s][0] != -1) {
+                int a = finds[s][0], b = finds[s][1];
+                boolean result = ds.find(a) == ds.find(b);
+                bw.write(result ? "YES\n" : "NO\n");
+            }
+        }
+        else {
+            int m = (s+e)>>1;
+            dnc(s,m,n*2);
+            dnc(m+1,e,n*2+1);
+        }
+
+        for(int[] edge : edges[n]) {
+            ds.rollback();
+        }
+    }
+
+}
+```