Construct Binary Tree from Preorder and Inorder Traversal

最新推荐文章于 2024-08-14 16:51:40 发布

最新推荐文章于 2024-08-14 16:51:40 发布 · 119 阅读

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本文介绍了一种通过前序遍历和中序遍历构建二叉树的方法。利用递归方式，根据前序遍历的第一个元素在中序遍历中的位置确定左右子树范围，进而构建完整的二叉树。

Given preorder and inorder traversal of a tree, construct the binary tree.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
    	return buildTree(preorder, 0, preorder.length, inorder, 0, inorder.length);
    }

	private TreeNode buildTree(int[] preorder, int i, int length,
			int[] inorder, int j, int length2) {
		if (i>length-1 || j>length2-1) {
			return null;
		}
		int tmp = preorder[i];
		int index = 0;
		for (int k = j; k < length2; k++) {
			if (inorder[k] == tmp) {
				index = k;
				break;
			}
		}
		int len = index-j;
		TreeNode root = new TreeNode(tmp);
		root.left = buildTree(preorder, i+1, i+len+1, inorder, j, index);
		root.right = buildTree(preorder, i+1+len, length, inorder, index+1, length2);
		return root;
	}
}