本题要求按照先序遍历的顺序输出给定二叉树的叶结点。

函数接口定义：

void PreorderPrintLeaves( BinTree BT );

其中BinTree结构定义如下：

typedef struct TNode *Position;
typedef Position BinTree;
struct TNode{
    
    ElementType Data;
    BinTree Left;
    BinTree Right;
};

函数PreorderPrintLeaves应按照先序遍历的顺序输出给定二叉树BT的叶结点，格式为一个空格跟着一个字符。

裁判测试程序样例：

#include <stdio.h>
#include <stdlib.h>

typedef char ElementType;
typedef struct TNode *Position;
typedef Position BinTree;
struct TNode{
    
    ElementType Data;
    BinTree Left;
    BinTree Right;
};

BinTree CreatBinTree(); /* 实现细节忽略 */
void PreorderPrintLeaves( BinTree BT );

int main()
{
    
    BinTree BT = CreatBinTree();
    printf("Leaf nodes are:");
    PreorderPrintLeaves(BT);
    printf("\n");

    return 0;
}
/* 你的代码将被嵌在这里 */

输出样例（对于图中给出的树）：

Leaf nodes are: D E H I

解答

void PreorderPrintLeaves(BinTree BT){
    
        if(BT == NULL) return;
        if(BT->Left == NULL && BT->Right == NULL)
        printf(" %c",BT->Data);
        PreorderPrintLeaves(BT->Left);
       PreorderPrintLeaves(BT->Right);
}

完整的代码

完整的代码

#include <stdio.h>
#include <stdlib.h>

typedef char ElementType;
typedef struct TNode *Position;
typedef Position BinTree;
struct TNode{
    
    ElementType Data;
    BinTree Left;
    BinTree Right;
};

BinTree CreatBinTree(); /* 实现细节忽略 */
void PreorderPrintLeaves( BinTree BT );

int main()
{
    
    BinTree BT = CreatBinTree();
    printf("Leaf nodes are:");
    PreorderPrintLeaves(BT);
    printf("\n");

    return 0;
}
BinTree CreatBinTree() {
    
    ElementType dada;
    scanf("%c",&dada);
    if(dada =='-'){
    
        return NULL;
    }
    BinTree root = (BinTree) malloc(sizeof (struct TNode));
    root->Data = dada;
    root->Left = CreatBinTree();
    root->Right = CreatBinTree();
    return root;
}

void PreorderPrintLeaves(BinTree BT){
    
        if(BT == NULL) return;
        if(BT->Left == NULL && BT->Right == NULL)
        printf(" %c",BT->Data);
        PreorderPrintLeaves(BT->Left);
       PreorderPrintLeaves(BT->Right);
}