Add a solution to The Earliest Moment When Everyone Become Friends

Author: soapyigu

Graph/EarliestMomentFriends.swift

@@ -0,0 +1,43 @@
+/**
+ * Question Link: https://leetcode.com/problems/the-earliest-moment-when-everyone-become-friends/
+ * Primary idea: Classic Union Find, union every node until the count drops down to 1.
+ * 
+ * Time Complexity: O(nlogn), Space Complexity: O(n)
+ *
+ */
+
+class EarliestMomentFriends {
+    func earliestAcq(_ logs: [[Int]], _ n: Int) -> Int {
+        let logs = logs.sorted { $0[0] < $1[0] }
+        
+        var roots = Array(0..<n), count = n
+        
+        for log in logs {
+            let time = log[0], friend1 = log[1], friend2 = log[2]
+            
+            let root1 = find(friend1, roots)
+            let root2 = find(friend2, roots)
+            
+            if root1 != root2 {
+                roots[root1] = root2
+                count -= 1
+            }
+            
+            if count == 1 {
+                return time
+            }
+        }
+        
+        return -1
+    }
+    
+    private func find(_ node: Int, _ roots: [Int]) -> Int {
+        var node = node
+        
+        while node != roots[node] {
+            node = roots[node]
+        }
+        
+        return node
+    }
+}