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67 lines
1.9 KiB
67 lines
1.9 KiB
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二叉树相关
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---
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#### 目录
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1. #### [07. 重建二叉树](https://leetcode-cn.com/problems/zhong-jian-er-cha-shu-lcof/)
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#### [07. 重建二叉树](https://leetcode-cn.com/problems/zhong-jian-er-cha-shu-lcof/)
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```java
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class Solution {
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public TreeNode buildTree(int[] preorder, int[] inorder) {
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int n = preorder.length;
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if (n == 0) {
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return null;
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}
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int rootVal = preorder[0], rootIndex = 0;
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for (int i = 0; i < n; i++) {
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if (inorder[i] == rootVal) {
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rootIndex = i;
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break;
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}
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}
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TreeNode root = new TreeNode(rootVal);
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root.left = buildTree(Arrays.copyOfRange(preorder, 1, 1 + rootIndex),
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Arrays.copyOfRange(inorder, 0, rootIndex));
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root.right = buildTree(Arrays.copyOfRange(preorder, 1 + rootIndex, n),
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Arrays.copyOfRange(inorder, rootIndex + 1, n));
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return root;
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}
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}
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```
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```java
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class Solution {
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public TreeNode buildTree(int[] preorder, int[] inorder) {
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if (preorder == null || preorder.length == 0) {
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return null;
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}
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TreeNode root = new TreeNode(preorder[0]);
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int length = preorder.length;
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Stack<TreeNode> stack = new Stack<>();
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stack.push(root);
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int inorderIndex = 0;
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for (int i = 1; i < length; i++) {
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int preorderVal = preorder[i];
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TreeNode node = stack.peek();
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if (node.val != inorder[inorderIndex]) {
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node.left = new TreeNode(preorderVal);
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stack.push(node.left);
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} else {
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while (!stack.isEmpty() && stack.peek().val == inorder[inorderIndex]) {
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node = stack.pop();
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inorderIndex++;
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}
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node.right = new TreeNode(preorderVal);
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stack.push(node.right);
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}
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}
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return root;
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}
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}
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```
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