一.二叉树的遍历
1 #include<iostream> 2 #include<stack> 3 #include<queue> 4 using namespace std; 5 6 typedef struct Node 7 { 8 int elem; 9 struct Node *right; 10 struct Node *left; 11 }*TreeNode; 12 13 void InitTree(TreeNode &root) 14 { 15 int x; 16 cin >> x; 17 if(x < 0) 18 { 19 root = NULL; 20 return; 21 } 22 root = new Node; 23 24 root->elem = x; 25 InitTree(root->left); 26 InitTree(root->right); 27 } 28 29 void PreOrder(TreeNode root) 30 { 31 if (root != NULL) 32 { 33 cout << root->elem << " "; 34 PreOrder(root->left); 35 PreOrder(root->right); 36 } 37 } 38 39 void InOrder(TreeNode root) 40 { 41 if (root != NULL) 42 { 43 InOrder(root->left); 44 cout << root->elem << " "; 45 InOrder(root->right); 46 } 47 } 48 49 void PostOrder(TreeNode root) 50 { 51 if (root != NULL) 52 { 53 PostOrder(root->left); 54 PostOrder(root->right); 55 cout << root->elem << " "; 56 } 57 } 58 59 void LevelOrder(TreeNode root) 60 { 61 if (root != NULL) 62 { 63 queue<TreeNode> q; 64 q.push(root); 65 while (! q.empty()) 66 { 67 cout << q.front()->elem << " "; 68 if (q.front()->left != NULL) 69 q.push(q.front()->left); 70 if (q.front()->right != NULL) 71 q.push(q.front()->right); 72 q.pop(); 73 } 74 } 75 } 76 77 /* 78 从根节点开始，向左遍历节点并输出元素，把每一个节点的右孩子push到栈里 79 遍历到NULL后，出栈一个节点p 80 继续上述步骤 81 直到栈为空 82 */ 83 void NoRecursivePreOrder(TreeNode root) 84 { 85 if (root == NULL) 86 { 87 return; 88 } 89 stack<TreeNode> s; 90 s.push(root); 91 while (! s.empty()) 92 { 93 TreeNode p = s.top(); 94 s.pop(); 95 while (p != NULL) 96 { 97 cout << p->elem << " "; 98 if (p->right != NULL) 99 { 100 s.push(p->right); 101 } 102 p = p->left; 103 } 104 } 105 } 106 107 /* 108 把p节点的所有左孩子都入栈 109 遍历到NULL后，出栈一个节点p并输出元素,p=p->right 110 继续上述步骤 111 直到栈为空 112 */ 113 void NoRecursiveInOrder(TreeNode root) 114 { 115 if (root == NULL) 116 { 117 return; 118 } 119 stack<TreeNode> s; 120 TreeNode p = root; 121 while (!s.empty() || p != NULL) 122 { 123 while (p != NULL) 124 { 125 s.push(p); 126 p = p->left; 127 } 128 if (!s.empty()) 129 { 130 p = s.top(); 131 s.pop(); 132 cout<< p->elem << " "; 133 p = p->right; 134 } 135 } 136 } 137 138 /* 139 把p节点的所有左孩子都入栈 140 遍历到NULL后 141 若p->right=NULL或者p的右孩子遍历过了则出栈并输出 否则p=p->right重复操作 142 直到栈为空 143 */ 144 void NoRecursivePostOrder(TreeNode root) 145 { 146 if (root == NULL) 147 { 148 return; 149 } 150 151 stack<TreeNode> s; 152 TreeNode p = root; 153 TreeNode visited = NULL; 154 155 while (p != NULL || ! s.empty()) 156 { 157 while (p != NULL) 158 { 159 s.push(p); 160 p = p->left; 161 } 162 p = s.top(); 163 if(p->right == NULL || p->right == visited) 164 { 165 cout<< p->elem << " "; 166 visited = p; 167 s.pop(); 168 p = NULL; 169 } 170 else 171 p = p->right; // 否则访问右孩子 172 } 173 } 174 175 176 int main() 177 { 178 TreeNode root; 179 InitTree(root); 180 181 PreOrder(root); 182 cout << endl; 183 NoRecursivePreOrder(root); 184 cout << endl; 185 186 InOrder(root); 187 cout << endl; 188 NoRecursiveInOrder(root); 189 cout << endl; 190 191 PostOrder(root); 192 cout << endl; 193 NoRecursivePostOrder(root); 194 cout << endl; 195 196 LevelOrder(root); 197 cout << endl; 198 199 return 0; 200 }