剑指Offer04 重建二叉树

/*************************************************************************
> File Name: 04_Rebuild_BinaryTree.c
> Author: Juntaran
> Mail: JuntaranMail@gmail.com
> Created Time: 2016年08月29日 星期一 16时32分35秒
************************************************************************/

#include <stdio.h>
#include <malloc.h>

// 二叉树结构体
struct BinaryTree
{
int val;
struct BinaryTree* left;
struct BinaryTree* right;
};

void preorderPrintBinaryTree(struct BinaryTree* root)
{
if (root == NULL)
return;
printf("%d ", root->val);
preorderPrintBinaryTree(root->left);
preorderPrintBinaryTree(root->right);
}

void inorderPrintBinaryTree(struct BinaryTree* root)
{
if (root == NULL)
return;
preorderPrintBinaryTree(root->left);
printf("%d ", root->val);
preorderPrintBinaryTree(root->right);
}

void postorderPrintBinaryTree(struct BinaryTree* root)
{
if (root == NULL)
return;
preorderPrintBinaryTree(root->left);
preorderPrintBinaryTree(root->right);
printf("%d ", root->val);
}

struct BinaryTree* rebuild_BinaryTree(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder)
{
// 前序遍历第一个数字是根节点的值
int rootValue = startPreorder[0];
struct BinaryTree* root = (BinaryTree*)malloc(sizeof(BinaryTree));
root->val = rootValue;
root->left = NULL;
root->right = NULL;

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

// 在前序遍历中找根节点的值
int* rootInorder = startInorder;
while (rootInorder<=endInorder && *rootInorder!=rootValue)
++ rootInorder;

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

struct BinaryTree* rebuild(int* preorder, int* inorder, int length)
{
if (preorder==NULL || inorder==NULL || length<=0)
return NULL;

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

// ====================测试代码====================
void Test(int* preorder, int* inorder, int length)
{
printf("The preorder sequence is: ");
for(int i = 0; i < length; ++ i)
printf("%d ", preorder[i]);
printf("\n");

printf("The inorder  sequence is: ");
for(int i = 0; i < length; ++ i)
printf("%d ", inorder[i]);
printf("\n");

struct BinaryTree* root = rebuild(preorder, inorder, length);

printf("After rebuild:\n");
printf("\nThe preorder  sequence is: ");
preorderPrintBinaryTree(root);
printf("\nThe inorder   sequence is: ");
inorderPrintBinaryTree(root);
printf("\nThe postorder sequence is: ");
postorderPrintBinaryTree(root);
}

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

Test(preorder, inorder, length);
}