[剑指offer][第三章][18]Subtree

[LintCode]Subtree

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param T1, T2: The roots of binary tree.
     * @return: True if T2 is a subtree of T1, or false.
     */
    public boolean isSubtree(TreeNode t1, TreeNode t2) {
        // 2016-04-08
        if (t2 == null) {
            return true;
        }
        if (t1 == null) {
            return false;
        }
        if (isSameTree(t1, t2)) {
            return true;
        }
        return isSubtree(t1.left, t2) || isSubtree(t1.right, t2);
    }
    
    /**
     * 判断两棵树是否完全一样（结构一样，值一样）
     */
    private boolean isSameTree(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) {
            return true;
        }
        if (t1 == null || t2 == null) {
            return false;
        }
        if (t1.val != t2.val) {
            return false;
        }
        return isSameTree(t1.left, t2.left) && isSameTree(t1.right, t2.right);
    }
}