Create vertical-order-traversal-of-a-binary-tree.cpp

Author: kamyu104

C++/vertical-order-traversal-of-a-binary-tree.cpp

@@ -0,0 +1,42 @@
+// Time:  O(nlogn)
+// Space: O(n)
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    using Lookup = map<int, map<int, multiset<int>>>;
+
+    vector<vector<int>> verticalTraversal(TreeNode* root) {
+        Lookup lookup;
+        dfs(root, &lookup, 0, 0);
+        vector<vector<int>> result;
+        for (const auto& kvp1 : lookup) {
+            vector<int> report;
+            for (const auto& kvp2 : kvp1.second) {
+                for (const auto& x : kvp2.second) {
+                    report.emplace_back(x);
+                }
+            }
+            result.emplace_back(move(report));
+        }
+        return result;
+    }
+
+private:
+    void dfs(TreeNode *root, Lookup *lookup, int x, int y){
+        if (!root) {
+            return;
+        }
+        (*lookup)[x][y].emplace(root->val);
+        dfs(root->left, lookup, x - 1, y + 1);
+        dfs(root->right, lookup, x + 1, y + 1);
+    }
+};