From b3d832abbe563f6b9430c26f6e97fffc0d76d893 Mon Sep 17 00:00:00 2001
From: oncsr <khj20006@naver.com>
Date: Thu, 20 Mar 2025 15:15:06 +0900
Subject: [PATCH] =?UTF-8?q?[20250320]=20BOJ=20/=20G1=20/=20Lifeguards=20(S?=
 =?UTF-8?q?ilver)=20/=20=EA=B6=8C=ED=98=81=EC=A4=80?=
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---
 .../202503/20 BOJ G1 Lifeguards (Silver).md   | 80 +++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 khj20006/202503/20 BOJ G1 Lifeguards (Silver).md

diff --git a/khj20006/202503/20 BOJ G1 Lifeguards (Silver).md b/khj20006/202503/20 BOJ G1 Lifeguards (Silver).md
new file mode 100644
index 00000000..b9e74f1a
--- /dev/null
+++ b/khj20006/202503/20 BOJ G1 Lifeguards (Silver).md	
@@ -0,0 +1,80 @@
+```java
+
+import java.util.*;
+import java.io.*;
+
+class Main {
+	
+	// IO field
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	static StringTokenizer st = new StringTokenizer("");
+
+	static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+	static String nextToken() throws Exception {
+		if(!st.hasMoreTokens()) nextLine();
+		return st.nextToken();
+	}
+	static int nextInt() throws Exception { return Integer.parseInt(nextToken()); }
+	static long nextLong() throws Exception { return Long.parseLong(nextToken()); }
+	static double nextDouble() throws Exception { return Double.parseDouble(nextToken()); }
+	static void bwEnd() throws Exception {bw.flush();bw.close();}
+	
+	// Additional field
+	
+	static int N;
+	static PriorityQueue<int[]> Q = new PriorityQueue<>((a,b) -> {
+		if(a[0] == b[0]) return b[1]-a[1];
+		return a[0]-b[0];
+	});
+	
+	public static void main(String[] args) throws Exception {
+		
+		ready();
+		solve();
+	
+		bwEnd();
+		
+	}
+	
+	static void ready() throws Exception{
+		
+		N = nextInt();
+		for(int i=0;i<N;i++) {
+			int a = nextInt(), b = nextInt();
+			Q.offer(new int[] {a,1,i});
+			Q.offer(new int[] {b,-1,i});
+		}
+		
+	}
+	
+	static void solve() throws Exception{
+
+		int tot = 0;
+		int[] len = new int[N];
+		int pos = 0;
+		TreeSet<Integer> T = new TreeSet<>();
+		while(!Q.isEmpty()) {
+			int prev = T.size();
+			if(prev == 1) len[T.first()] += Q.peek()[0]-pos;
+			if(prev > 0) tot += Q.peek()[0]-pos;
+			int now = Q.peek()[0];
+			while(!Q.isEmpty() && Q.peek()[0] == now) {
+				int info = Q.peek()[1];
+				if(info == 1) T.add(Q.poll()[2]);
+				else T.remove(Q.poll()[2]);
+			}
+			pos = now;
+		}
+		
+		int ans = 0;
+		for(int i=0;i<N;i++) ans = Math.max(ans, tot-len[i]);
+		bw.write(ans + "\n");
+		
+		
+		
+	}
+	
+}
+
+```