题目地址：http://acm.hdu.edu.cn/showproblem.php?pid=3999

本题为简单二叉排序树，先按排序树创建树，然后先序遍历二叉树，输出的时候最后一个数字后面没有空格。

数组实现：

#include<stdio.h>
#include<string.h>
#define N 100005
int tree[N],left[N],right[N],a[N],num,flg;//tree数组用来保存树节点的值，left，right数组用来保存结点的左右子树，
void insert(int index,int x)
{if( x <= tree[index] )//当根结点比x的值大 的时候。{if(left[index] == -1)//当根结点左子树为空的时候。left[index] = flg;elseinsert(left[index],x);//左子树不为空时继续遍历左子树}else{if(right[index] == -1)//当右子树为空时right[index] = flg;elseinsert(right[index],x);//当右子树不为空的时候}
}
void PreOrderTraverse(int index)//先序遍历二叉排序树
{a[num++] = tree[index];if(left[index] != -1)PreOrderTraverse(left[index]);if(right[index] != -1)PreOrderTraverse(right[index]);
}
int main()
{int n,i,x,root;while(~scanf("%d",&n)){//初始化树的所有结点都为空。memset(left,-1,sizeof(left));memset(right,-1,sizeof(right));root = -1;flg = 0;for(i = 0; i< n; i++){scanf("%d",&x);if(root == -1)tree[++root] = x;else{tree[++flg] = x;insert(root,x);}}num = 0;PreOrderTraverse(root);printf("%d",a[0]);for(i = 1; i <= n -1; i++)printf(" %d",a[i]);printf("\n");}return 0;
}

动态创建二叉树排序树

#include<stdio.h>
#include<stdlib.h>
struct node
{int data;struct node *left;struct node *right;
};
int b[100005],num,n;
void delete_tree(node *t)
{if(t->left)delete_tree(t->left);if(t->right)delete_tree(t->left);free(t);
}
node* insert(node *t,int x)
{if(t){if(x < t->data)t->left = insert(t->left,x);elset->right = insert(t->right,x);}else{t = (node*)malloc(sizeof(node));t->data = x;t->left = t->right = NULL;}return t;
}
void PreOrderTraverse(node *t)
{if(t == NULL)return ;b[num++] = t->data;PreOrderTraverse(t->left);PreOrderTraverse(t->right);free(t);
}
node *create(node *t)
{int i,x;for(i = 0; i < n; i++){scanf("%d",&x);t = insert(t,x);}return t;
}
int main()
{int i;node *root;while(~scanf("%d",&n)){root = NULL;root = create(root);num = 0;PreOrderTraverse(root);printf("%d",b[0]);for(i = 1; i < n; i++)printf(" %d",b[i]);printf("\n");}return 0;
}