diff --git "a/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2169] \353\241\234\353\264\207 \354\241\260\354\242\205\355\225\230\352\270\260.md" "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2169] \353\241\234\353\264\207 \354\241\260\354\242\205\355\225\230\352\270\260.md"
new file mode 100644
index 00000000..70bccee8
--- /dev/null
+++ "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2169] \353\241\234\353\264\207 \354\241\260\354\242\205\355\225\230\352\270\260.md"	
@@ -0,0 +1,66 @@
+```java
+import java.util.*;
+import java.io.*;
+
+public 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 {
+        while(!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, M;
+    static int[][] A, dp, left, right;
+
+    public static void main(String[] args) throws Exception {
+
+        ready();
+        solve();
+
+        bwEnd();
+
+    }
+
+    static void ready() throws Exception{
+
+        N = nextInt();
+        M = nextInt();
+        A = new int[N+2][M+2];
+        for(int i=1;i<=N;i++) for(int j=1;j<=M;j++) A[i][j] = nextInt();
+        dp = new int[N+2][M+2];
+        Arrays.fill(dp[0], -(int)1e9);
+        left = new int[N+2][M+2];
+        right = new int[N+2][M+2];
+        right[1][M+1] = -(int)1e9;
+        for(int i=2;i<=N;i++){
+            left[i][0] = -(int)1e9;
+            right[i][M+1] = -(int)1e9;
+        }
+
+    }
+
+    static void solve() throws Exception {
+
+        for(int i=1;i<=N;i++) {
+            for(int j=1;j<=M;j++) left[i][j] = Math.max(left[i][j-1], dp[i-1][j]) + A[i][j];
+            for(int j=M;j>=1;j--) right[i][j] = Math.max(right[i][j+1], dp[i-1][j]) + A[i][j];
+            for(int j=1;j<=M;j++) dp[i][j] = Math.max(left[i][j], right[i][j]);
+        }
+        bw.write(dp[N][M] + "\n");
+
+    }
+
+}
+```
diff --git "a/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2461] \353\214\200\355\221\234 \354\204\240\354\210\230.md" "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2461] \353\214\200\355\221\234 \354\204\240\354\210\230.md"
new file mode 100644
index 00000000..33e9e234
--- /dev/null
+++ "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-2461] \353\214\200\355\221\234 \354\204\240\354\210\230.md"	
@@ -0,0 +1,88 @@
+```java
+import java.util.*;
+import java.io.*;
+
+public 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 {
+		while(!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 class Node{
+	    int cur, nxt, row, col;
+	    Node(int cur, int nxt, int row, int col){
+	        this.cur = cur;
+	        this.nxt = nxt;
+	        this.row = row;
+	        this.col = col;
+	    }
+	}
+	
+	static int N, M;
+	static int[][] A;
+	
+	public static void main(String[] args) throws Exception {
+		
+		ready();
+		solve();
+		
+		bwEnd();
+		
+	}
+	
+	static void ready() throws Exception{
+		
+		N = nextInt();
+		M = nextInt();
+		A = new int[N][M];
+		for(int i=0;i<N;i++){
+		    for(int j=0;j<M;j++) A[i][j] = nextInt();
+		    Arrays.sort(A[i]);
+		}
+		
+	}
+	
+	static void solve() throws Exception {
+		
+	    PriorityQueue<Node> Q = new PriorityQueue<>((a,b) -> {
+	        if(a.cur == b.cur){
+	            if(a.nxt == -1) return 1;
+	            if(b.nxt == -1) return -1;
+	            return a.nxt - b.nxt;
+	        }
+	        return a.cur - b.cur;
+	    });
+	    
+	    int e = -1;
+	    for(int i=0;i<N;i++) {
+	        Q.offer(new Node(A[i][0], 1<M ? A[i][1] : -1, i, 1));
+	        e = Math.max(e, A[i][0]);
+	    }
+	    int ans = e-Q.peek().cur;
+	    while(Q.peek().nxt != -1){
+	        Node now = Q.poll();
+	        e = Math.max(e, now.nxt);
+	        Q.offer(new Node(now.nxt, now.col+1 < M ? A[now.row][now.col+1] : -1, now.row, now.col+1));
+	        ans = Math.min(ans, e-Q.peek().cur);
+	    }
+	    bw.write(ans + "\n");
+		
+		
+		
+	}
+	
+}
+```
diff --git "a/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9470] Strahler \354\210\234\354\204\234.md" "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9470] Strahler \354\210\234\354\204\234.md"
new file mode 100644
index 00000000..4010b626
--- /dev/null
+++ "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9470] Strahler \354\210\234\354\204\234.md"	
@@ -0,0 +1,83 @@
+```java
+import java.util.*;
+import java.io.*;
+
+public 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 {
+        while(!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 K, M, P;
+    static int[] d;
+    static List<Integer>[] V, C;
+
+    public static void main(String[] args) throws Exception {
+
+        int T = nextInt();
+        for(int t=1;t<=T;solve(t++)) ready();
+
+        bwEnd();
+
+    }
+
+    static void ready() throws Exception{
+
+        K = nextInt();
+        M = nextInt();
+        P = nextInt();
+        V = new List[M+1];
+        C = new List[M+1];
+        for(int i=1;i<=M;i++) {
+            V[i] = new ArrayList<>();
+            C[i] = new ArrayList<>();
+        }
+        d = new int[M+1];
+        for(int i=0;i<P;i++) {
+            int a = nextInt(), b = nextInt();
+            V[a].add(b);
+            d[b]++;
+        }
+
+    }
+
+    static void solve(int tc) throws Exception {
+
+        Queue<Integer> Q = new LinkedList<>();
+        for(int i=1;i<=M;i++) if(d[i] == 0) {
+            Q.offer(i);
+            C[i].add(1);
+        }
+
+        while(!Q.isEmpty()) {
+            int n = Q.poll();
+            Collections.sort(C[n], (a,b) -> b-a);
+            int c = C[n].get(0);
+            if(C[n].size() > 1 && C[n].get(0).equals(C[n].get(1))) c++;
+            if(n == M){
+                bw.write(tc + " " + c + "\n");
+                return;
+            }
+            for(int i:V[n]) {
+                if(--d[i] == 0) Q.offer(i);
+                C[i].add(c);
+            }
+        }
+
+    }
+
+}
+```
diff --git "a/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9576] \354\261\205 \353\202\230\353\210\240\354\243\274\352\270\260.md" "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9576] \354\261\205 \353\202\230\353\210\240\354\243\274\352\270\260.md"
new file mode 100644
index 00000000..319bb928
--- /dev/null
+++ "b/\352\266\214\355\230\201\354\244\200_18\354\243\274\354\260\250/[BOJ-9576] \354\261\205 \353\202\230\353\210\240\354\243\274\352\270\260.md"	
@@ -0,0 +1,68 @@
+```java
+import java.util.*;
+import java.io.*;
+
+public 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 {
+        while(!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, M;
+    static int[][] A;
+    static boolean[] received;
+
+    public static void main(String[] args) throws Exception {
+
+        for(int T=nextInt();T-->0;solve()) ready();
+
+        bwEnd();
+
+    }
+
+    static void ready() throws Exception{
+
+        N = nextInt();
+        M = nextInt();
+        A = new int[M][2];
+        received = new boolean[M];
+        for(int i=0;i<M;i++) for(int j=0;j<2;j++) A[i][j] = nextInt();
+
+    }
+
+    static void solve() throws Exception {
+
+        int cnt = 0;
+        for(int i=1;i<=N;i++){
+            int emin = 12345, idx = -1;
+            for(int j=0;j<M;j++) if(!received[j] && A[j][0] <= i && A[j][1] >= i) {
+                if(A[j][1] < emin){
+                    emin = A[j][1];
+                    idx = j;
+                }
+            }
+            if(idx != -1) {
+                received[idx] = true;
+                cnt++;
+            }
+
+        }
+        bw.write(cnt + "\n");
+
+    }
+
+}
+```