二叉树的前序、中序、后序及层次遍历的递归与非递归源码实现

二叉树是基本却非常重要的数据结构，经常在面试中出现，现在我主要是针对面试中出现比率非常高的前序、中序、后序及层次遍历，给出自己的递归与非递归实现，源码仅供参考。

另外，如果觉得我写的好，可以关注我的github帐号(https://github.com/chenqiangzhishen). 本文代码部分我也贴在了如下的目录中。

(https://github.com/chenqiangzhishen/Algorithms/blob/master/binaryTree/binaryTree.c)

有了github，我会经常更新些新的，高效的，经典的算法和其他新的知识与大家分享，开源快乐～

注：我的代码不出意外，都可以直接运行，采用gcc/g++/gdb进行的开发与调试工具及vim开发工具。

因为比较喜欢在Linux下编程，不大喜欢用中文切来切去的进行描述，所以直接采用英文进行注释。

#include <stdio.h>
#include <stdlib.h>
#define MAX 100
typedef struct BiTNode {
int data;
struct BiTNode *lchild, *rchild;
} BiTNode, *BiTree;
BiTNode* stack[MAX];

BiTree createBiTree(void)
{
int data;
BiTNode *root = NULL;
scanf("%d", &data);

if(data == -1)
{
root = NULL;
}
else
{
root = (BiTNode *)malloc(sizeof(BiTNode));
root->data = data;
root->lchild = createBiTree();
root->rchild = createBiTree();
}
return root;
}

void preOrderTraverse(BiTree root)
{
if(root == NULL)
return;
printf("%d ", root->data);
preOrderTraverse(root->lchild);
preOrderTraverse(root->rchild);
}

void inOrderTraverse(BiTree root)
{
if(root == NULL)
return;
inOrderTraverse(root->lchild);
printf("%d ", root->data);
inOrderTraverse(root->rchild);
}

void postOrderTraverse(BiTree root)
{
if(root == NULL)
return;
postOrderTraverse(root->lchild);
postOrderTraverse(root->rchild);
printf("%d ", root->data);
}

void preOrderTraverse_none_recursive(BiTree root)
{
if(root == NULL)
return;
int top = 0;
while(root || top>0)
{
while(root)
{
printf("%d ", root->data);
stack[top++] = root;
root = root->lchild;
}
root = stack[--top];
root = root->rchild;
}
printf("\n");
}

void inOrderTraverse_none_recursive(BiTree root)
{
if(root == NULL)
return;
int top = 0;
while(root || top>0)
{
while(root)
{
stack[top++] = root;
root = root->lchild;
}
root = stack[--top];
printf("%d ", root->data);
root = root->rchild;
}
printf("\n");
}

void postOrderTraverse_none_recursive(BiTree root)
{
if(root == NULL)
return;
BiTNode *visited = NULL;
int top = 0;
while(root || top>0)
{
while(root)
{
stack[top++] = root;
root = root->lchild;
}
root = stack[top -1];
//if do not have right child or the right child is visited, then visit the parent(root) node.
if(root->rchild==NULL || visited==root->rchild)
{
printf("%d ", root->data);
visited = root;
--top;
root = NULL;//note that: let the node become NULL
}
else
{
root = root->rchild;
}
}
printf("\n");
}

void levelTraverse(BiTree root)
{
if(root == NULL)
return;
BiTNode* p = NULL;
int top = 0;
int beg = 0;
stack[top++] = root;
int end = top;
while(beg < end)
{
while(beg < end)
{
p = stack[beg++];
printf("%d ", p->data);
if(p->lchild)
stack[top++] = p->lchild;
if(p->rchild)
stack[top++] = p->rchild;
}
end = top;
}
}

int main(void)
{

printf("please input the data to create binary tree, input -1 to exit\n");
BiTree root = createBiTree();
printf("The binary tree is:\n");

printf("The preOrderTraverse is:\n");
preOrderTraverse(root);
printf("\n");
printf("The inOrderTraverse is:\n");
inOrderTraverse(root);
printf("\n");
printf("The postOrderTraverse is:\n");
postOrderTraverse(root);
printf("\n");
printf("The preOrderTraverse with none recursive is:\n");
preOrderTraverse_none_recursive(root);
printf("The inOrderTraverse with none recursive is:\n");
inOrderTraverse_none_recursive(root);
printf("The postOrderTraverse with none recursive is:\n");
postOrderTraverse_none_recursive(root);
printf("The level traverse for binary tree is:\n");
levelTraverse(root);
printf("\n");
return 0;
}