题解 | #重建二叉树#

/**

• Definition for binary tree
• public class TreeNode {

• int val;
  

• TreeNode left;
  

• TreeNode right;
  

• TreeNode(int x) { val = x; }
  

• } / import java.util.;

public class Solution { public TreeNode reConstructBinaryTree(int [] pre,int [] vin) { return construct(pre, vin); }

public static TreeNode construct(int [] pre,int [] vin){
    if(pre.length == 0){
        return null;
    }
    
    if(pre.length == 1){
        return new TreeNode(pre[0]);
    }
    
    int pos = find(vin, pre[0]);
    
    int[] pre1 = Arrays.copyOfRange(pre, 1, pos+1);
    int[] pre2 = Arrays.copyOfRange(pre, pos+1, pre.length);
    int[] vin1 = Arrays.copyOfRange(vin, 0, pos);
    int[] vin2 = Arrays.copyOfRange(vin, pos+1, pre.length);
    
    TreeNode curHead = new TreeNode(pre[0]);
    TreeNode left = construct(pre1, vin1);
    TreeNode right = construct(pre2, vin2);
    
    curHead.left = left;
    curHead.right = right;
    
    return curHead;
    
}

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

}