二叉树的非递归遍历（先序、中序、后序和层序遍历）

 1 typedef struct TreeNode *BinTree;
 2 struct TreeNode {
 3     char Data;
 4     BinTree Left;
 5     BinTree Right;
 6 };
 7 
 8 BinTree CreateBinTree(BinTree T)
 9 {
10     char c;
11     scanf("%c", &c);
12     if ( c != ‘#‘ ) {
13         T = (BinTree)malloc(sizeof(struct TreeNode));
14         T->Data = c;
15         T->Left = CreateBinTree(T->Left);
16         T->Right = CreateBinTree(T->Right);
17     }
18     else {
19         T = NULL;
20     }
21     return T;
22 }

 1 void PreOrderTraverse(BinTree BT)
 2 {
 3     BinTree T = BT;
 4     Stack S = CreateStack();    /* 创建并初始化堆栈  */
 5     while ( T || !IsEmpty(S) ) {
 6         while ( T ) {         /* 一直向左并将沿途节点压入栈底  */
 7             printf("%c ", T->Data);    /* 打印节点数据 */
 8             Push(S, T);
 9             T = T->Left;  
10         }
11         if ( !IsEmpty(S) ) {
12             T = Pop(S);            /* 节点弹出堆栈 */ 
13             T = T->Right;        /* 转向右子树 */ 
14         }
15     }
16 }

 1 void InOrderTraverse(BinTree BT)
 2 {
 3     BinTree T = BT;
 4     Stack S = CreateStack();    /* 创建并初始化堆栈  */
 5     while ( T || !IsEmpty(S) ) {
 6         while ( T ) {         /* 一直向左并将沿途节点压入栈底  */
 7             Push(S, T);
 8             T = T->Left;  
 9         }
10         if ( !IsEmpty(S) ) {
11             T = Pop(S);            /* 节点弹出堆栈 */ 
12             printf("%c ", T->Data);    /* 打印节点数据 */
13             T = T->Right;        /* 转向右子树 */ 
14         }
15     }
16 }

struct Node {
    BinTree BT;
    char Tag;
};
typedef struct Node *PtrToNode;

void PostOrderTraverse(BinTree T)
{
    BinTree P = T;
    struct Node *PNode;
    Stack S = CreateStack();
    
    while ( P || !IsEmpty(S) ) {
        // 遍历左子树 
        while ( P ) {
            PNode = (struct Node*)malloc(sizeof(struct Node));
            PNode->BT = P;
            PNode->Tag = ‘L‘;    //  第一次被标记 
            Push(S, PNode);
            P = P->Left;
        }
        // 栈不空 并且  栈顶元素 是第二次被标记 
        while ( !IsEmpty(S) && GetTop(S)->Tag == ‘R‘ ) {
            PNode = Pop(S);
            printf("%c ", PNode->BT->Data);
        }
        
        if ( !IsEmpty(S) ) {
            PNode = GetTop(S);
            PNode->Tag = ‘R‘;    // 第二次被标记 
            P = PNode->BT;
            P = P->Right;         // 转向右子树 
        }
    }
}

 1 void LevelOrderTraverse(BinTree BT)
 2 {
 3     Queue Q;
 4     ElementType T;
 5     
 6     if ( !BT )    return;    // 若是空树则返回 
 7     
 8     Q = CreateQueue();    // 创建空队列  
 9     AddQ(Q, BT);
10     while ( !IsEmpty(Q) ) {
11         T = DeleteQ(Q);
12         printf("%c ", T->Data);
13         if ( T->Left )    AddQ(Q, T->Left);
14         if ( T->Right ) AddQ(Q, T->Right);
15     }
16 }