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  • [LC] 572. Subtree of Another Tree

    Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

    Example 1:
    Given tree s:

         3
        / 
       4   5
      / 
     1   2
    

    Given tree t:

       4 
      / 
     1   2
    

    Return true, because t has the same structure and node values with a subtree of s.

    Example 2:
    Given tree s:

         3
        / 
       4   5
      / 
     1   2
        /
       0
    

    Given tree t:

       4
      / 
     1   2
    

    Return false.

    Solution:

    Time: O(M *N)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        public boolean isSubtree(TreeNode s, TreeNode t) {
            if (s == null) {
                return false;
            }
            if (isSameTree(s, t)) {
                return true;
            }
            return isSubtree(s.left, t) || isSubtree(s.right, t);
        }
        
        private boolean isSameTree(TreeNode s, TreeNode t) {
            if (s == null && t == null) {
                return true;
            }
            if (s == null || t == null) {
                return false;
            }
            if (s.val != t.val) {
                return false;
            }
            return isSameTree(s.left, t.left) && isSameTree(s.right, t.right);
        }
    }
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  • 原文地址:https://www.cnblogs.com/xuanlu/p/12148684.html
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