保持先序遍歷不變，加一個特殊判斷是否左右節點為空即可。（注意葉子結點一定是左右孩子均為空）

下面給出AC程式碼：

#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(); /* 實現細節忽略 */
void PreorderPrintLeaves( BinTree BT );

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

    return 0;
}

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