From 11abda6b569164ef0ec6825907c9ca24117d7b49 Mon Sep 17 00:00:00 2001
From: songyc macbook <gitea@gitea>
Date: Mon, 1 Dec 2025 21:02:17 +0900
Subject: [PATCH] baekjoon 20251201

---
 code_study/Baekjoon/swift/2252.swift | 36 ++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 code_study/Baekjoon/swift/2252.swift

diff --git a/code_study/Baekjoon/swift/2252.swift b/code_study/Baekjoon/swift/2252.swift
new file mode 100644
index 0000000..5f9196d
--- /dev/null
+++ b/code_study/Baekjoon/swift/2252.swift
@@ -0,0 +1,36 @@
+if let input1 = readLine(),
+   let NM = input1.split(separator: " ").compactMap({Int($0)}) as? [Int],
+   let N = NM.first, let M = NM.last
+{
+    var graph: [[Int]] = Array(repeating: [], count: N+1)
+    var inDegree = Array(repeating: 0, count: N+1)
+    
+    for _ in 1...M {
+        guard let input2 = readLine(),
+              let uv = input2.split(separator: " ").compactMap({Int($0)}) as? [Int],
+              let u = uv.first, let v = uv.last
+        else { break }
+        
+        graph[u].append(v)
+        inDegree[v] += 1
+    }
+    
+    var qu: [Int] = []
+    var idx = 0
+    
+    for n in 1...N {
+        if inDegree[n] == 0 { qu.append(n) }
+    }
+    
+    while idx < qu.count {
+        let num = qu[idx]
+        idx += 1
+        
+        for nxt in graph[num] {
+            inDegree[nxt] -= 1
+            if inDegree[nxt] == 0 { qu.append(nxt) }
+        }
+    }
+    
+    print(qu.map{ String($0) }.joined(separator: " "))
+}