[leetcode]Construct Binary Tree from Preorder and Inorder Traversal

 

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
    TreeNode *buildTree(vector<int> &pre, int preStart, vector<int> &in, int inStart, int len){
        if (preStart<0 || preStart+len>pre.size() || inStart<0 || inStart+len>in.size() || len<1)
            return NULL;

        TreeNode *root = new TreeNode(pre[preStart]);
        int i = 0;
        for (i = 0; i < len; i++)
            if (in[inStart + i] == root->val)
                break;

        int leftLen = i;
        int rightLen = len - 1 - leftLen;

        root->left = buildTree(pre, preStart+1, in, inStart, leftLen);
        root->right = buildTree(pre, preStart+1+leftLen, in, inStart+leftLen+1, rightLen);

        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.size() != inorder.size() || preorder.size()<1)
            return NULL;

        return buildTree(preorder, 0, inorder, 0, inorder.size());
    }
};

 

 

 

 

 

 

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