重建二叉树

Posted 2020-07-27 mokayy

/*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。/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    struct TreeNode* ConstructBinaryTree(vector<int> pre,int preStart,int preEnd,vector<int> in,int inStart,int inEnd) {
       
        TreeNode* root = new TreeNode(pre[preStart]);
        if((preEnd == preStart)&&(inEnd == inStart)&&(in[inStart]==pre[preStart]))
            return  root;
        int i = inStart;
        while((i<=inEnd)&&(in[i]!=pre[preStart])){
            i++;
            
        }
        int lenf = i -inStart;
        int lenr = inEnd - i ;
        int leftpreEnd = preStart+lenf ;
        if(lenf>0){
            root->left = ConstructBinaryTree(pre,preStart+1,leftpreEnd,in,inStart,i-1);
        }
        if(lenr>0){
            root->right = ConstructBinaryTree(pre,leftpreEnd+1,preEnd,in,i+1,inEnd);
        }
        
        return root;
        
    }
    struct TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> in) {
        int len = pre.size();
        if(len == 0)  return NULL;
        return ConstructBinaryTree(pre,0,len-1,in,0,len-1);
        
       
    }
};