Create delete-tree-nodes.cpp

Author: kamyu104

C++/delete-tree-nodes.cpp

@@ -0,0 +1,42 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int deleteTreeNodes(int nodes, vector<int>& parent, vector<int>& value) {
+        unordered_map<int, vector<int>> children;
+        for (int i = 1; i < parent.size(); ++i) {
+            children[parent[i]].emplace_back(i);
+        }
+        return dfs(value, &children, 0).second;
+    }
+
+private:
+    pair<int, int> dfs(const vector<int>& value, 
+                       unordered_map<int, vector<int>> *children,
+                       int x) {
+        int total = value[x], count = 1;
+        for (const auto& y : (*children)[x]) {
+            const auto& [t, c] = dfs(value, children, y);
+            total += t;
+            count += t ? c : 0;
+        }
+        return {total, total ? count : 0};
+    }
+};
+
+
+// Time:  O(n)
+// Space: O(n)
+class Solution2 {
+public:
+    int deleteTreeNodes(int nodes, vector<int>& parent, vector<int>& value) {
+        // assuming parent[i] < i for all i > 0
+        vector<int> result(nodes, 1);
+        for (int i = nodes - 1; i >= 1; --i) {
+            value[parent[i]] += value[i];
+            result[parent[i]] += value[i] ? result[i] : 0;
+        }
+        return result[0];
+    }
+};