"Binary Tree Preorder Traversal"

Author: lennylxx

src/144.cpp

@@ -0,0 +1,57 @@
+#include <iostream>
+#include <vector>
+#include <stack>
+
+using namespace std;
+
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution {
+public:
+    vector<int> preorderTraversal(TreeNode *root) {
+        vector<int> ret;
+        if (!root) return ret;
+
+        stack<TreeNode *> s;
+        s.push(root);
+
+        while (!s.empty()) {
+            TreeNode *p = s.top();
+            s.pop();
+
+            if (p) {
+                ret.push_back(p->val);
+                s.push(p->right);
+                s.push(p->left);
+            }
+        }
+        return ret;
+    }
+};
+
+int main() {
+    TreeNode *root = new TreeNode(4);
+    TreeNode *p = root;
+
+    p->left = new TreeNode(2);
+    p->right = new TreeNode(5);
+    p = p->left;
+    p->left = new TreeNode(1);
+    p->right = new TreeNode(3);
+
+    Solution s;
+    vector<int> ret = s.preorderTraversal(root);
+
+    // should be 42135
+    for (unsigned int i = 0; i < ret.size(); i++) {
+        cout << ret[i];
+    }
+    cout << endl;
+
+    return 0;
+}