Create maximum-level-sum-of-a-binary-tree.cpp

Author: kamyu104

C++/maximum-level-sum-of-a-binary-tree.cpp

@@ -0,0 +1,68 @@
+// Time:  O(n)
+// Space: O(h)
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+// dfs solution
+class Solution {
+public:
+    int maxLevelSum(TreeNode* root) {
+        vector<int> level_sums;
+        dfs(root, 0, &level_sums);
+        return distance(level_sums.cbegin(),
+                        max_element(level_sums.cbegin(), level_sums.cend())) + 1;
+    }
+
+private:
+    void dfs(TreeNode *node, int i, vector<int> *level_sums) {
+        if (!node) {
+            return;
+        }
+        if (i == level_sums->size()) {
+            level_sums->emplace_back();
+        }
+        (*level_sums)[i] += node->val;
+        dfs(node->left, i + 1, level_sums);
+        dfs(node->right, i + 1, level_sums);
+    }
+};
+
+// Time:  O(n)
+// Space: O(w)
+// bfs solution
+class Solution2 {
+public:
+    int maxLevelSum(TreeNode* root) {
+        int result = 0, level = 1, max_total = numeric_limits<int>::min();
+        queue<TreeNode*> q({root});
+        while (!q.empty()) {
+            queue<TreeNode*> next_q;
+            int total = 0;
+            while (!q.empty()) {
+                const auto node = q.front(); q.pop();
+                total += node->val;
+                if (node->left) {
+                    next_q.emplace(node->left);
+                }
+                if (node->right) {
+                    next_q.emplace(node->right);
+                }
+            }
+            if (total > max_total) {
+                max_total = total;
+                result = level;
+            }
+            q = move(next_q);
+            ++level;
+        }
+        return result;
+    }
+};