二叉树遍历

limitsy · limitsy · commit a719a1bd2e74 · 2019-05-04T16:44:24.000+08:00
diff --git a/notes/数据结构与算法.md b/notes/数据结构与算法.md
@@ -174,6 +174,116 @@ private static int searchDfs(int[] data, int l, int r, int target) {
 
 #### 深度优先遍历（前序、中序、后序遍历）
 
+```C++
+/**
+ * 前序遍历 非递归实现
+ * 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:
+    vector<int> preorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        TreeNode* node = root;
+        stack<TreeNode*> s;
+        map<TreeNode*, bool> M;
+        if(node != NULL) {
+            s.push(node);
+            while (!s.empty()) {
+                node = s.top();
+                if (!M[node]) {
+                    ans.push_back(node->val);
+                    M[node] = true;
+                }
+                if (node->left != NULL) {
+                    s.push(node->left);
+                    node->left = NULL;
+                } else if (node->right != NULL) {
+                    s.push(node->right);
+                    node->right = NULL;
+                } else {
+                    s.pop();
+                }
+            }
+        }
+        return ans;
+    }
+};
+```
+
+```c++
+/**
+ * 中序遍历
+ * 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:
+    vector<int> inorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        if(root != NULL) {
+            traversal(root, ans);
+        }
+        return ans;
+    }
+    
+    void traversal(TreeNode* node, vector<int> &ans) {
+        if(node->left != NULL) {
+            traversal(node->left, ans);
+        }
+        ans.push_back(node->val);
+        if(node->right != NULL) {
+            traversal(node->right, ans);
+        }
+    }
+};
+```
+
+
+
+```c++
+/**
+ * 后序遍历
+ * 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:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        if(root != NULL) {
+            traversal(root, ans);
+        }
+        return ans;
+    }
+
+    void traversal(TreeNode* node, vector<int> &ans) {
+        if(node->left != NULL) {
+            traversal(node->left, ans);
+        }
+        if(node->right != NULL) {
+            traversal(node->right, ans);
+        }
+        ans.push_back(node->val);
+    }
+};
+```
+
 #### 广度优先遍历（层序遍历）
 
 ### 5. AVL树
