leetcode/DS_Tree/106+buildTree.cpp at master · DuanYaQi/leetcode · GitHub

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* build(vector<int>& inorder, int inStart, int inEnd,
                vector<int>& postorder, int postStart, int postEnd) {
        if (postStart > postEnd) {
            return nullptr;
        }
        int index = inStart;
        for (int i = inStart; i <= inEnd; i++) {
            if (inorder[i] == postorder[postEnd]) {
                index = i;
            }
        }
        TreeNode* root = new TreeNode(postorder[postEnd]);

        root->left = build(inorder, inStart, index - 1,
                        postorder, postStart, postStart + index - inStart - 1);
        root->right = build(inorder, index + 1, inEnd,
                        postorder, postStart + index - inStart, postEnd - 1);
        return root;
    }

    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        return build(inorder, 0, inorder.size()-1, postorder, 0, postorder.size()-1);
    }
};