2006年清华大学计算机研究生机试真题

http://ac.jobdu.com/problem.php?pid=1078 二叉树遍历

#include<stdio.h>
#include<string.h>

//二叉树结点的描述   
typedef struct BinaryTreeNode  
{
	char data;
	struct BinaryTreeNode *lchild, *rchild;      //左右孩子   
}BinaryTreeNode,*BinaryTree;

inline BinaryTreeNode* ConstructCore(char *startPreorder, char *endPreorder, char *startInorder, char *endInorder)
{
	//前序遍历序列的第一个字符是根节点的值
	char rootValue = startPreorder[0];
	BinaryTreeNode* root = new BinaryTreeNode();
	root->data = rootValue;
	root->lchild = root->rchild = NULL;

	if(startPreorder == endPreorder)
	{
		if(startInorder == endInorder && *startPreorder== *startInorder)
			return root;
	}

	//在中序遍历中找到根节点的值
	char *rootInorder = startInorder;
	while(rootInorder <= endInorder && *rootInorder != rootValue)
		rootInorder++;

	int leftLength = rootInorder - startInorder;
	char *leftPreorderEnd = startPreorder + leftLength;
	if(leftLength > 0)
	{
		//构建左子树
		root->lchild = ConstructCore(startPreorder+1, leftPreorderEnd, startInorder, rootInorder-1);
	}
	if(leftLength < endPreorder - startPreorder)
	{
		//构建右子树
		root->rchild = ConstructCore(leftPreorderEnd+1, endPreorder, rootInorder+1, endInorder);
	}
	return root;
}

//分别在前序遍历和中序遍历的序列中确定左、右子树的子序列
inline BinaryTreeNode* Construct(char *preorder, char *inorder, int length)
{
	if(preorder == NULL || inorder == NULL || length<=0)
		return NULL;
	return ConstructCore(preorder, preorder+length-1, inorder, inorder+length-1);
}

//后序遍历 
inline void PostOrder(BinaryTreeNode *root)  
{
	if(root==NULL)
		return ;
	PostOrder(root->lchild);        //递归调用，前序遍历左子树
	PostOrder(root->rchild);        //递归调用，前序遍历右子树
	printf("%c", root->data);      //输出数据
}

//释放二叉树
inline void DeleteBinaryTree(BinaryTree root)
{
	if(root)
	{
		DeleteBinaryTree(root->lchild);    //释放左子树
		DeleteBinaryTree(root->rchild);    //释放右子树
		delete root;          //释放根结点
	}
}

int main(void)
{
	int length;
	char preorder[27],inorder[27];
	while(scanf("%s",preorder)!=EOF)
	{
		scanf("%s",inorder);
		length = strlen(preorder);
		BinaryTreeNode* root = Construct(preorder, inorder, length);
		PostOrder(root);
		printf("\n");
		DeleteBinaryTree(root);
	}
	return 0;
}