[radiantchoi] WEEK 11 Solutions

graph-valid-tree/radiantchoi.py

@@ -0,0 +1,34 @@
+from typing import List
+
+# 어떤 그래프가 Valid Tree려면?
+# 순환이 발생하지 않으면서, 모든 노드가 연결되어 있어야 한다.
+# n개의 노드를 모두 연결하는 데 필요한 간선의 갯수는 n - 1개
+# 순환 발생 탐지 -> Union Find
+
+class Solution:
+    def find(self, parent: List[int], n: int) -> int:
+        if parent[n] == n:
+            return n
+
+        parent[n] = self.find(parent, parent[n])
+        return parent[n]
+
+    def union(self, parent: List[int], left: int, right: int) -> bool:
+        left_parent = self.find(parent, left)
+        right_parent = self.find(parent, right)
+
+        if left_parent == right_parent:
+            return False
+
+        parent[right_parent] = left_parent
+        return True
+
+    def valid_tree(self, n: int, edges: List[List[int]]) -> bool:
+        parents = list(range(n))
+
+        for edge in edges:
+            # Union Find에서 False가 반환된다는 것은 순환이 발생한다는 것
+            if not self.union(parents, edge[0], edge[1]):
+                return False
+
+        return len(edges) == n - 1

missing-number/radiantchoi.ts

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+function missingNumber(nums: number[]): number {
+    let occurence = new Map<number, boolean>();
+
+    for (let i = 0; i <= nums.length; i++) {
+        occurence.set(i, false);
+    }
+
+    for (const num of nums) {
+        occurence.set(num, true);
+    }
+
+    const results = Array.from(occurence.entries());
+
+    for (const result of results) {
+        if (result[1] === false) {
+            return result[0];
+        }
+    }
+
+    return 0;
+};