17、树的子结构

题目描述
输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        if(root1==null||root2==null){
            return false;
        }
        boolean ret = false;
        if(root1.val==root2.val){
            ret = isSubTree(root1,root2);
        }
        if(!ret){
            ret = HasSubtree(root1.left,root2);
            if(!ret){
                ret = HasSubtree(root1.right,root2);
            }
        }
       
        return ret;
    }
        
    
    
    public boolean isSubTree(TreeNode root1,TreeNode root2){
        if(root2==null){
            return true;
        }
        if(root1==null&&root2!=null){
            return false;
        }
        if(root1.val == root2.val){
            boolean left = isSubTree(root1.left,root2.left);
            boolean right = isSubTree(root1.right,root2.right);
            return left&&right;
        }
        return false;
    }

测试代码

public static void main(String[] args) {
        TreeNode root1 = new TreeNode(8);
        root1.left = new TreeNode(8);
        root1.right = new TreeNode(7);
        root1.left.left = new TreeNode(9);
        root1.left.right = new TreeNode(2);

        TreeNode root2 = new TreeNode(8);
        root2.left  = new TreeNode(9);
        root2.right = new TreeNode(2);

        System.out.println(HasSubtree(root1,root2));

    }
``

2017.6.1 第二次做

/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;

public TreeNode(int val) {
    this.val = val;

}

}
*/
public class Solution {
public boolean HasSubtree(TreeNode root1,TreeNode root2) {
if(root1==null || root2==null){
return false;
}

    return IsSubtree(root1,root2) ||HasSubtree(root1.left,root2)||HasSubtree(root1.right,root2);

}

public boolean IsSubtree(TreeNode root1, TreeNode root2){
    if(root1==null && root2==null){
        return true;
    }
    if(root1==null && root2 !=null){
        return false;
    }
    if(root1!=null && root2 ==null){
        return true;
    }
    if(root1.val!=root2.val){
        return false;
    }
    
    return IsSubtree(root1.left,root2.left) && IsSubtree(root1.right,root2.right);
}

}