leetcode之Construct Binary Tree from Preorder and Inorder Traversal

最新推荐文章于 2024-01-17 14:50:43 发布

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本文介绍了一种使用前序遍历和中序遍历构建二叉树的方法。通过递归算法，解析两个遍历序列，逐步构建出完整的二叉树结构。

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/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
    TreeNode *buildCore(vector<int> &preorder, int prebeg, int preend,
    vector<int> &inorder, int inbeg, int inend) {
       int root_data = preorder[prebeg];
       TreeNode* root = new TreeNode(root_data);
       if (prebeg == preend) {
           return root;
       }
       int leftSize=0, rightSize=0;
       for (int i = inbeg; i < inend && inorder[i]!=root_data; i++) {
            leftSize++;
       }
       /*if (leftSize==0 && rightSize==0) {
           return NULL;
       }*/
       rightSize = preend-prebeg-leftSize;
       TreeNode* left = NULL;
       TreeNode* right = NULL;
       if (leftSize!=0) {
           left = buildCore(preorder, prebeg+1, leftSize+prebeg, inorder, inbeg, leftSize+inbeg-1);
       }
       if (rightSize!=0) {
           right = buildCore(preorder, prebeg+leftSize+1, preend, inorder, leftSize+inbeg+1, inend);
       }

       root->left = left;
       root->right = right;
       return root;
    }
    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (preorder.empty() && inorder.empty()) {
            return NULL;
        }
        return buildCore(preorder, 0, preorder.size()-1, inorder, 0, inorder.size()-1);
    }
};