LeetCode 106. Construct Binary Tree from Inorder and Postorder Traversal

最新推荐文章于 2023-11-14 11:05:42 发布

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本文介绍了一种通过中序遍历和后序遍历构建二叉树的算法。该算法首先找到根节点，并递归地构建左右子树。关键在于正确确定每个子树的索引范围。

The most important thing is to find the correct index.

void build(vector<int>& postorder, vector<int>& inorder, int index, int begin, int end, TreeNode*& root) {
  if(begin >= end) return;
  int n = postorder.size();
  int val = postorder[index];
  root = new TreeNode(val);
  int i = 0;
  while(i < n && inorder[i] != val) {i++;}
  if(i > 0) build(postorder, inorder, i + index - end, begin, i, root->left);
  if(i < n - 1) build(postorder, inorder, index - 1, i + 1, end, root->right);
}

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