04 重建二叉树

Posted 2021-03-17 ruanshuai

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        return reConstructBinaryTree(pre, 0, pre.length - 1, in, 0, in.length - 1);
    }

    public TreeNode reConstructBinaryTree(int[] pre, int startPre, int endPre, int[] in, int startIn, int endIn){
        if(startPre > endPre || startIn > endIn){
            return null;
        }
        TreeNode root = new TreeNode(pre[startPre]);
        for(int i = startIn; i <= endIn; i++){
            if(in[i] == pre[startPre]){
                root.left = reConstructBinaryTree(pre, startPre + 1, startPre + i, in, startIn, i - 1);
                root.right = reConstructBinaryTree(pre, i - startIn + startPre + 1, endPre, in, i + 1, endIn);
            }
        }
        return root;
    }
}

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