二叉树构造

题目：

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

public:
int FindValPtr(vector<int> arr, int val)
{
int i = 0;
for (i = 0; i < arr.size(); i++)
{
if (arr[i] == val)
{
return i;
}
}
return i;
}

/* 查找子树的根节点 */
public:
void FindSubTreeNode(int type, struct TreeNode* p_node, vector<int> pre_arr, int pre_start, int pre_end,
vector<int> mid_arr, int mid_start, int mid_end)
{
int ptr = 0;
int l_count = 0;
int r_count = 0;
struct TreeNode* root_n = (struct TreeNode*)malloc(sizeof(struct TreeNode));
if (pre_start <= pre_end)
{
root_n->val = pre_arr[pre_start];
root_n->left = NULL;
root_n->right = NULL;
}
else
{
return;
}
ptr = FindValPtr(mid_arr, root_n->val);
l_count = ptr - mid_start;
r_count = mid_end - ptr;
type ? (p_node->right = root_n) : (p_node->left = root_n);
FindSubTreeNode(0, root_n, pre_arr, pre_start+1, pre_start+l_count, mid_arr, mid_start, ptr-1);
FindSubTreeNode(1, root_n, pre_arr, pre_start+l_count+1, pre_end, mid_arr, ptr+1, mid_end);
}

public:
struct TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> in)
{
int ptr = 0;
struct TreeNode* root_n = (struct TreeNode*)malloc(sizeof(struct TreeNode));
if (pre.size() > 0)
{
root_n->val = pre[0];
root_n->left = NULL;
root_n->right = NULL;
}
ptr = FindValPtr(in, root_n->val);
FindSubTreeNode(0, root_n, pre, 1, ptr, in, 0, ptr-1);
FindSubTreeNode(1, root_n, pre, ptr+1, pre.size()-1, in, ptr+1, in.size()-1);
return root_n;
}