二叉树的遍历

这里为了方便，以二叉查找树为例：

#include<stdio.h>#include<malloc.h>#define M 25struct BST{int Data;BST *left;BST *right;};BST *stack[M];//栈int flag[M];//后序遍历中需要用到的标记数组bool AddNodeToBST(BST* &Root, int Value){if(Root == NULL){BST *Node = (BST *)malloc(sizeof(BST));if(!Node){printf("内存分配失败\n");return false;}Node->Data = Value;Node->left = NULL;Node->right = NULL;Root = Node;return true;}else if(Root->Data > Value)AddNodeToBST(Root->left,Value);else if(Root->Data < Value)AddNodeToBST(Root->right, Value);else{printf("重复加入节点\n");return false;}}void Destory(BST *Root){if(!Root)return;Destory(Root->left);Destory(Root->right);free(Root);Root = NULL;}//递归前序遍历，先根，再左，后右void PreOrderRe(BST *Root){if(!Root)return;printf("%d ",Root->Data);PreOrderRe(Root->left);PreOrderRe(Root->right);}//递归的中序遍历，先左，再根，后右void MidOrderRe(BST *Root){if(!Root)return;MidOrderRe(Root->left);printf("%d ",Root->Data);MidOrderRe(Root->right);}//递归的后序遍历，先左，再右，后根void PostOrderRe(BST *Root){if(!Root)return;PostOrderRe(Root->left);PostOrderRe(Root->right);printf("%d ", Root->Data);}void PreOrder(BST *Root){if(!Root)return;BST *p;int top = -1;p = Root;while(p != NULL || top > -1){while(p != NULL){printf("%d ",p->Data);stack[++top] = p;p = p->left;}//由于叶节点的左右都为空，所以遇到叶节点的时候会弹出两次。遇到左空，弹本身，遇到右空，弹出父节点//三种遍历的思想是一样的if(top > -1){p = stack[top]->right;--top;}}printf("\n");}void MidOrder(BST *Root){if(!Root)return;int top = -1;BST *p = Root;while(p != NULL || top > -1){while(p != NULL){stack[++top] = p;p = p->left;}if(top > -1){printf("%d ", stack[top]->Data);p = stack[top]->right;--top;}}printf("\n");}void PostOrder(BST *Root){int top = -1;BST *p = Root;while(p != NULL || top > -1){while(p != NULL){stack[++top] = p;flag[top] = 0;p = p->left;}while(top > -1 && flag[top]){printf("%d ", stack[top]->Data);--top;}if(top > -1){flag[top] = 1;p = stack[top]->right;}}printf("\n");}void main(){BST *Root = NULL;int Value;//输入数据while(scanf("%d", &Value)){if(Value <= 0)break;AddNodeToBST(Root, Value);}PreOrderRe(Root);printf("\n");PreOrder(Root);MidOrderRe(Root);printf("\n");MidOrder(Root);PostOrderRe(Root);printf("\n");PostOrder(Root);Destory(Root);}

运行结果：

PS：二叉树的层次遍历，这里的stack数组如上定义，实际上是用的队列。

void LevelOrder(BST *Root){if(!Root)return;int head = 1;int tail = 1;stack[tail] = Root;flag[0] = 0;flag[1] = 1;while(head <= tail){if(flag[head - 1] < flag[head])printf("\n");printf("%d ", stack[head]->Data);if(stack[head]->left){stack[++tail] = stack[head]->left;flag[tail] = flag[head] + 1;}if(stack[head]->right){stack[++tail] = stack[head]->right;flag[tail] = flag[head] + 1;}++head;}printf("\n");}

结果：
10
5 15
3 8 14 17
1 4 7 9 16 18