100. Same Tree

Link

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

T: O(N)

Example 1:

Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Solution

遞迴方式求解，將問題縮解成兩個子樹的比較，但要注意q , p為null的情形

class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {     
        if(p == null && q == null) return true;
        else if( p == null || q == null) return false;
        return p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}