先序輸出葉結點（15 分）

輸出葉子結點，就是找一個結點的左兒子和右兒子都為空，輸出就可以

#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(); /* 實作細節忽略 */
void PreorderPrintLeaves( BinTree BT );

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

    return 0;
}
/* 你的代碼将被嵌在這裡 */
void PreorderPrintLeaves( BinTree BT )
{
    if(BT == NULL)
    {
        return;
    }
    if(BT->Left == NULL && BT->Right == NULL)
        printf(" %c",BT->Data);
    if(BT->Left)
        PreorderPrintLeaves(BT ->Left);
    if(BT->Right)
        PreorderPrintLeaves(BT ->Right);
}