劍指offer-->面試題6 重建二叉樹

下面是源代碼：

#include <stdio.h>

struct BinaryTreeNode
{
	int m_nValue;
	BinaryTreeNode *m_pLeft;
	BinaryTreeNode *m_pRight;
};

BinaryTreeNode *ConstructCore(int *startPreorder, int *endPreorder, int *startInorder, int *endInorder)
{
	int rootValue = startPreorder[0];
	BinaryTreeNode *root = new BinaryTreeNode();
	root->m_nValue = rootValue;
	root->m_pLeft = NULL;
	root->m_pRight = NULL;

	//遞歸結束條件，當只剩節點時
	if(startPreorder == endPreorder)
	{
		if(startInorder == endInorder && *startPreorder == *startInorder)
		{
			return root;
		}else
		{
			return NULL;
		}
	}

	int *rootInorder = startInorder;
	while(rootInorder <= endInorder && *rootInorder != rootValue)
	{
		rootInorder++;
	}

	if(rootInorder > endInorder)
	{
		printf("無效的輸入\n");
	}

	int leftLength = rootInorder - startInorder;
	int rightLength = endInorder - rootInorder;

	if(leftLength > 0)
	{
		root->m_pLeft = ConstructCore(startPreorder + 1, startPreorder + leftLength, startInorder, startInorder + leftLength - 1);
	}

	if(rightLength > 0)
	{
		root->m_pRight = ConstructCore(startPreorder + leftLength + 1, endPreorder, rootInorder + 1, endInorder);
	}

	return root;
}

BinaryTreeNode *Construct(int *preorder, int *inorder, int length)
{
	if(preorder == NULL, inorder == NULL, length <= 0)
	{
		return NULL;
	}

	return ConstructCore(preorder, preorder + length - 1, inorder, inorder + length - 1);
}

void PrintTreeNode(BinaryTreeNode* pNode)
{
    if(pNode != NULL)
    {
        printf("value of this node is: %d\n", pNode->m_nValue);

        if(pNode->m_pLeft != NULL)
            printf("value of its left child is: %d.\n", pNode->m_pLeft->m_nValue);
        else
            printf("left child is null.\n");

        if(pNode->m_pRight != NULL)
            printf("value of its right child is: %d.\n", pNode->m_pRight->m_nValue);
        else
            printf("right child is null.\n");
    }
    else
    {
        printf("this node is null.\n");
    }

    printf("\n");
}

void PrintTree(BinaryTreeNode* pRoot)
{
    PrintTreeNode(pRoot);

    if(pRoot != NULL)
    {
        if(pRoot->m_pLeft != NULL)
            PrintTree(pRoot->m_pLeft);

        if(pRoot->m_pRight != NULL)
            PrintTree(pRoot->m_pRight);
    }
}

void DestroyTree(BinaryTreeNode* pRoot)
{
    if(pRoot != NULL)
    {
        BinaryTreeNode* pLeft = pRoot->m_pLeft;
        BinaryTreeNode* pRight = pRoot->m_pRight;

        delete pRoot;
        pRoot = NULL;

        DestroyTree(pLeft);
        DestroyTree(pRight);
    }
}

void main()
{
	const int length = 8;
	int preorder[length] = {1, 2, 4, 7, 3, 5, 6, 8};
	int inorder[length] = {4, 7, 2, 1, 5, 3, 8, 6};

	BinaryTreeNode *root = Construct(preorder, inorder, length);
	PrintTree(root);
	DestroyTree(root);
}

下面是運行結果：