From 5737de5c2b1b4554ae550b57c3043ec2e060b22a Mon Sep 17 00:00:00 2001
From: songyc macbook <gitea@gitea>
Date: Mon, 17 Nov 2025 20:36:22 +0900
Subject: [PATCH] 20251117 baekjoon

---
 code_study/Baekjoon/swift/20040.swift | 54 +++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 code_study/Baekjoon/swift/20040.swift

diff --git a/code_study/Baekjoon/swift/20040.swift b/code_study/Baekjoon/swift/20040.swift
new file mode 100644
index 0000000..c084f8e
--- /dev/null
+++ b/code_study/Baekjoon/swift/20040.swift
@@ -0,0 +1,54 @@
+struct Union_Find {
+    var root: [Int]
+    
+    init(_ N: Int) {
+        self.root = Array(0...N)
+    }
+    
+    mutating func find(_ x: Int) -> Int {
+        if x == root[x] {
+            return x
+        }
+        
+        root[x] = find(root[x])
+        return root[x]
+    }
+    
+    mutating func union(_ a: Int, _ b: Int) {
+        let x = find(a)
+        let y = find(b)
+        
+        if x>=y {
+            root[x] = y
+        }
+        else {
+            root[y] = x
+        }
+    }
+    
+    mutating func same_root(_ x: Int, _ y: Int) -> Bool {
+        return find(x) == find(y)
+    }
+}
+
+if let input = readLine(),
+   let nums = input.split(separator: " ").compactMap({Int($0)}) as? [Int],
+   let N = nums.first, let M = nums.last
+{
+    var uf = Union_Find(N)
+    
+    var result = 0
+    for m in 1...M {
+        guard let line = readLine(),
+              let point = line.split(separator: " ").map({Int($0)}) as? [Int],
+              let a = point.first, let b = point.last else { break }
+        
+        if uf.same_root(a, b) {
+            result = m
+            break
+        }
+        uf.union(a, b)
+     }
+    
+    print(result)
+}