【剑指Offer】树的子结构

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题目

输入两棵二叉树A和B，判断B是不是A的子结构。

实现

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

    public TreeNode(int val) {
        this.val = val;
    }
}
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public boolean HasSubtree(TreeNode root1, TreeNode root2) {
    boolean result = false;

    if (root1 != null && root2 != null){
        if (root1.val == root2.val)
            result = DoesTree1HasTree2(root1, root2);

        if (result == false)
            result = HasSubtree(root1.left, root2);

        if (result == false)
            result = HasSubtree(root1.right, root2);
    }

    return result;
}

private boolean DoesTree1HasTree2(TreeNode root1, TreeNode root2){
    if (root2 == null)
        return true;
    else if (root1 == null)
        return false;
    else if (root1.val != root2.val)
        return false;
    
    return DoesTree1HasTree2(root1.left, root2.left) && DoesTree1HasTree2(root1.right, root2.right);
}