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二叉树的遍历

  1 struct TreeNode {
  2     char val;
  3     TreeNode *left;
  4     TreeNode *right;
  5     int visitCount;        //节点访问次数,后序遍历会用到
  6     TreeNode(char c) : val(c), left(NULL), right(NULL), visitCount(0) {}
  7 };
  8 
  9 //先序遍历_非递归
 10 void PreOrderTraverse(TreeNode *root)
 11 {
 12     if (root == NULL)
 13         return;
 14 
 15     stack<TreeNode*> node_stack;
 16     TreeNode *p = root;
 17     while (p || !node_stack.empty()) {
 18         if (p) {
 19             cout << p->val << ' ';
 20             node_stack.push(p);
 21             p = p->left;
 22         } else {
 23             p = node_stack.top();
 24             node_stack.pop();
 25             p = p->right;
 26         }
 27     }
 28 }
 29 
 30 //先序遍历_递归
 31 void PreOrderTraverse_1(TreeNode *root)
 32 {
 33     if (root == NULL)
 34         return;
 35     cout << root->val << ' ';
 36     PreOrderTraverse_1(root->left);
 37     PreOrderTraverse_1(root->right);
 38 }
 39 
 40 //中序遍历_非递归
 41 void InOrderTraverse(TreeNode *root)
 42 {
 43     if (root == NULL)
 44         return;
 45 
 46     stack<TreeNode*> node_stack;
 47     TreeNode *p = root;
 48     while (p || !node_stack.empty()) {
 49         if (p) {
 50             node_stack.push(p);
 51             p = p->left;
 52         } else {
 53             p = node_stack.top();
 54             node_stack.pop();
 55             cout << p->val << ' ';
 56             p = p->right;
 57         }
 58     }
 59 }
 60 
 61 //中序遍历_递归
 62 void InOrderTraverse_1(TreeNode *root)
 63 {
 64     if (root == NULL)
 65         return;
 66     InOrderTraverse_1(root->left);
 67     cout << root->val << ' ';
 68     InOrderTraverse_1(root->right);
 69 }
 70 
 71 //后序遍历_非递归
 72 void PostOrderTraverse(TreeNode *root)
 73 {
 74     if (root == NULL)
 75         return;
 76 
 77     stack<TreeNode*> node_stack;
 78     TreeNode *p = root;
 79     while (p || !node_stack.empty()) {
 80         if (p) {
 81             p->visitCount = 1;
 82             node_stack.push(p);
 83             p = p->left;
 84         } else {
 85             p = node_stack.top();
 86             node_stack.pop();
 87             if (p->visitCount == 2) {
 88                 cout << p->val << ' ';
 89                 p = NULL;
 90             } else {
 91                 p->visitCount++;
 92                 node_stack.push(p);
 93                 p = p->right;
 94             }
 95         }
 96     }
 97 }
 98 
 99 //后序遍历_递归
100 void PostOrderTraverse_1(TreeNode *root)
101 {
102     if (root == NULL)
103         return;
104     PostOrderTraverse_1(root->left);
105     PostOrderTraverse_1(root->right);
106     cout << root->val << ' ';
107 }
108 
109 //层序遍历
110 void LevelOrderTraverse(TreeNode *root)
111 {
112     if (root == NULL)
113         return;
114 
115     queue<TreeNode*> node_queue;
116     node_queue.push(root);
117     while (!node_queue.empty()) {
118         TreeNode *p = node_queue.front();
119         node_queue.pop();
120         cout << p->val << ' ';
121 
122         if (p->left)
123             node_queue.push(p->left);
124         if (p->right)
125             node_queue.push(p->right);
126     }
127 }

以下图二叉树为例：

 1 void CreateBiTree(TreeNode* &T)
 2 {
 3     char ch;
 4     cin >> ch;
 5     if (ch == '#') {
 6         T = NULL;
 7     } else {
 8         T = new TreeNode(ch);
 9         CreateBiTree(T->left);
10         CreateBiTree(T->right);
11     }
12 }
13 
14 int main()
15 {
16     TreeNode *root;
17     CreateBiTree(root);
18 
19     cout << "先序遍历_非递归: " << endl;
20     PreOrderTraverse(root);
21     cout << endl;
22     cout << "先序遍历_递归: " << endl;
23     PreOrderTraverse_1(root);
24     cout << endl;
25 
26     cout << "中序遍历_非递归: " << endl;
27     InOrderTraverse(root);
28     cout << endl;
29     cout << "中序遍历_递归: " << endl;
30     InOrderTraverse_1(root);
31     cout << endl;
32 
33     cout << "后序遍历_非递归: " << endl;
34     PostOrderTraverse(root);
35     cout << endl;
36     cout << "后序遍历_递归: " << endl;
37     PostOrderTraverse_1(root);
38     cout << endl;
39 
40     cout << "层序遍历: " << endl;
41     LevelOrderTraverse(root);
42     cout << endl;
43 
44     return 0;
45 }

结果如下：

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原文地址：https://www.cnblogs.com/mengwang024/p/4632443.html