遍历二叉树

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二叉树遍历：

访问节点：

void Visit(BTNode* pNode){std::cout << pNode->nData << " ";}

前序遍历：

// 前序遍历（递归）void PreOrderTraverse1(BTNode* pRoot){if (NULL == pRoot)return;Visit(pRoot);PreOrderTraverse1(pRoot->pLeft);PreOrderTraverse1(pRoot->pRight);}// 前序遍历（非递归）void PreOrderTraverse2(BTNode* pRoot){if (NULL == pRoot)return;BTNode * pCur =pRoot;std::stack<BTNode*> myStack;while (pCur != NULL || !myStack.empty()){while (pCur != NULL) // 将所有左子树入栈{Visit(pCur);myStack.push(pCur);pCur = pCur->pLeft;}if (!myStack.empty()) // 取栈顶元素，对其右子树进行处理{pCur = myStack.top();myStack.pop();pCur = pCur->pRight;}}}// 前序遍历（非递归）void PreOrderTraverse3(BTNode* pRoot){if (NULL == pRoot)return;BTNode* pCur = NULL;std::stack<BTNode*> myStack;myStack.push(pRoot);while (!myStack.empty()){pCur = myStack.top();Visit(pCur);myStack.pop();// 先入栈右子树if (pCur->pRight != NULL)myStack.push(pCur->pRight);// 后入栈左子树if (pCur->pLeft != NULL)myStack.push(pCur->pLeft);}}

中序遍历：

// 中序遍历（非递归）void InOrderTraverse2(BTNode* pRoot){if (NULL == pRoot)return;BTNode* pCur = pRoot;std::stack<BTNode*> myStack;while (pCur != NULL || !myStack.empty()){// 将当前节点的左子树入栈while (pCur != NULL){myStack.push(pCur);pCur = pCur->pLeft;}if (! myStack.empty()){pCur = myStack.top();myStack.pop();Visit(pCur);pCur = pCur->pRight;}}}

后序遍历：

// 后序遍历（递归）void PostOrderTraverse1(BTNode* pRoot){if (NULL == pRoot)return;PostOrderTraverse1(pRoot->pLeft);PostOrderTraverse1(pRoot->pRight);Visit(pRoot);}// 后序遍历（非递归）void PostOrderTraverse2(BTNode* pRoot){if (NULL == pRoot)return;BTNode* pCur = NULL;BTNode* pPre = NULL; // 用来标识前一个访问节点std::stack<BTNode*> myStack;myStack.push(pRoot); // 入栈根节点while (!myStack.empty()){pCur = myStack.top();// 如果左右子树为空，或者左右子树均已访问if (NULL == pCur->pLeft && NULL == pCur->pRight ||pPre != NULL && (pPre == pCur->pLeft || pPre == pCur->pRight)){Visit(pCur);myStack.pop();pPre = pCur; // 标识pCur节点已访问}else{/*先入栈右子树，再入栈左子树。出栈的时候才能先访问左子树，在访问右子树*/if (pCur->pRight != NULL)myStack.push(pCur->pRight);if (pCur->pLeft != NULL)myStack.push(pCur->pLeft);}}}

层序遍历:

// 层序遍历void LevelOrderTraverse(BTNode* pRoot){if (NULL == pRoot)return;BTNode* pCur = NULL;std::queue<BTNode*> myQueue;myQueue.push(pRoot); // 先将根节点入队while (!myQueue.empty()){pCur = myQueue.front(); // 取队首节点Visit(pCur);myQueue.pop();if (pCur->pLeft != NULL)  // 入队左子树myQueue.push(pCur->pLeft);if (pCur->pRight != NULL) // 入队右子树myQueue.push(pCur->pRight);}}

参考文章：

算法之二叉树各种遍历

二叉树的非递归遍历

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