题解 | #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 {
    private static boolean IsSame(TreeNode begin,TreeNode beginSub) {
        if(beginSub == null) {
            return true;
        }
        if(begin == null) {
            return false;
        }
        if(begin.val != beginSub.val) {
            return false;
        }
        return IsSame(begin.left,beginSub.left) && IsSame(begin.right,beginSub.right);
    }

    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        if(root1 == null || root2 == null) {
            return false;
        }
        boolean ans = false;
        if(root1.val == root2.val) {//当val值相等，有机会是子结构，此时需要判定左右子树是否相等
            ans = IsSame(root1,root2);
        }

        if(!ans) {//说明上面判定失败，再看root1的左子树中有没有root2
            ans = HasSubtree(root1.left,root2);
        }
        if(!ans) {//说明上面判定失败，再看root1的右子树中有没有root2
            ans = HasSubtree(root1.right,root2);
        } 
        return ans;
    }
}