剑指offer九：重建二叉树

#include <iostream>
using namespace std;

struct binary_tree_node {
	int value;
	binary_tree_node*  left;
	binary_tree_node*  right;
};

binary_tree_node* binary_tree_constuct(int* preorder, int* inorder, int length);

int main()
{
	int pre[8] = { 1,2,4,7,3,5,6,8 };
	int in[8] = { 4,7,2,1,5,3,8,6 };

	binary_tree_node* root = binary_tree_constuct(pre, in, 8);
}

binary_tree_node* construct_method(int* preorder, int* endpreorder, int* inorder, int* endinorder)
{
	int root_value = preorder[0];
	binary_tree_node* root = new binary_tree_node();
    root->value = root_value;
	root->left = NULL;
	root->right = NULL;

	cout << root_value << " ";

	if (preorder == endpreorder && inorder == endinorder)
		return root;

	int* rootIndex = inorder;
	while (*rootIndex != root_value && rootIndex < endpreorder)
		rootIndex++;

	int left_len = rootIndex - inorder;
	int* left_preorder_end = preorder + left_len;
	//构建左子树
	if (left_len > 0)//左子树只要大于0就要构建右子树
	{
		root->left = construct_method(preorder + 1, left_preorder_end, inorder, rootIndex - 1);
	}
	//构建右子树
	if (endpreorder - preorder - left_len > 0)//右子树只要大于0就要构建右子树
	{
		root->right = construct_method(left_preorder_end + 1, endpreorder, rootIndex + 1, endinorder);
	}
	return root;
}

binary_tree_node* binary_tree_constuct(int* preorder, int* inorder, int length)
{
	if (preorder == NULL || inorder == NULL || length <= 0)
	{
		return NULL;
	}

	return construct_method(preorder, preorder + length - 1, inorder, inorder + length - 1);

}