[LeetCode] Construct Binary Tree from Inorder and Postorder Traversal

最新推荐文章于 2022-01-01 11:35:53 发布

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本文介绍了一种通过中序和后序遍历构建二叉树的方法。该方法利用递归过程，通过查找后序遍历中根节点的位置来划分中序序列，从而构建完整的二叉树结构。

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

Note:
You may assume that duplicates do not exist in the tree.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
		return build(inorder, 0, inorder.length - 1, postorder, 0, postorder.length - 1);
	}

	public TreeNode build(int[] inorder, int lo1, int hi1,
						 	int[] postorder, int lo2, int hi2) {
		if (lo2 > hi2) return null;

		int index = getIndex(inorder, postorder[hi2]);

		TreeNode root = new TreeNode(postorder[hi2]);
		root.left = build(inorder, lo1, index - 1, postorder, lo2, lo2 + ((index - 1) - lo1));
		root.right = build(inorder, index + 1, hi1, postorder,
				lo2 + ((index - 1) - lo1) + 1, lo2 + ((index - 1) - lo1) + 1 + (hi1 - (index + 1)));
		
		return root;
	}

	public int getIndex(int[] array, int val) {
		for (int i = 0; i < array.length; i++) {
			if (array[i] == val) return i;
		}

		return -1;
	}
}