Question

Formatted question description: https://leetcode.ca/all/100.html

Given the roots of two binary trees p and q, 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.

Example 1:

Input: p = [1,2,3], q = [1,2,3]
Output: true

Example 2:

Input: p = [1,2], q = [1,null,2]
Output: false

Example 3:

Input: p = [1,2,1], q = [1,1,2]
Output: false

Constraints:

The number of nodes in both trees is in the range [0, 100].
-10⁴ <= Node.val <= 10⁴

Algorithm

Depth first search DFS to recurse.

Code

public class Same_Tree {

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode(int x) { val = x; }
     * }
     */

    public class Solution_iteration {
        public boolean isSameTree(TreeNode p, TreeNode q) {
            if (p == null) {
                return q == null;
            }

            if (q == null) {
                return p == null;
            }

            Stack<TreeNode> sk1 = new Stack<TreeNode>();
            Stack<TreeNode> sk2 = new Stack<TreeNode>();

            sk1.push(p);
            sk2.push(q);

            while (!sk1.isEmpty() && !sk2.isEmpty()) {
                TreeNode current1 = sk1.pop();
                TreeNode current2 = sk2.pop();

                if (current1 == null && current2 == null) {
                    continue; // @note: missed both null check
                } else if (current1 == null && current2 != null) {
                    return false;
                } else if (current1 != null && current2 == null) {
                    return false;
                } else if (current1.val != current2.val) {
                    return false;
                }

                sk1.push(current1.left);
                sk2.push(current2.left);

                sk1.push(current1.right);
                sk2.push(current2.right);

            }

            // final check
            if (!sk1.isEmpty() || !sk2.isEmpty()) {
                return false;
            }

            return true;

        }
    }


    public class Solution_recursion {
        public boolean isSameTree(TreeNode p, TreeNode q) {

            if (p == null) {
                return q == null;
            }

            if (q == null) {
                return p == null;
            }

            if (p.val != q.val) {
                return false;
            }

            return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
        }
    }

}

############

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == q) return true;
        if (p == null || q == null || p.val != q.val) return false;
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}

// OJ: https://leetcode.com/problems/same-tree/
// Time: O(N)
// Space: O(H)
class Solution {
public:
    bool isSameTree(TreeNode* p, TreeNode* q) {
        return (!p && !q) || (p && q && p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right));
    }
};

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
  def isSameTree(self, p, q):
    """
    :type p: TreeNode
    :type q: TreeNode
    :rtype: bool
    """
    if not p or not q: 
      return p == q # covers: p=none and q!=none, q=none and p!=none, both none
    return p.val == q.val and self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)


# iteration
class Solution:
    def isSameTree(self, p: TreeNode, q: TreeNode) -> bool:
        if p is None:
            return q is None

        if q is None:
            return p is None

        stack1 = [p]
        stack2 = [q]

        while stack1 and stack2:
            current1 = stack1.pop()
            current2 = stack2.pop()

            if current1 is None and current2 is None:
                continue
            elif current1 is None or current2 is None:
                return False
            elif current1.val != current2.val:
                return False

            stack1.append(current1.left)
            stack2.append(current2.left)

            stack1.append(current1.right)
            stack2.append(current2.right)

        return not stack1 and not stack2

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
 func isSameTree(p *TreeNode, q *TreeNode) bool {
    if p == q {
        return true
    }
    if p == nil || q == nil || p.Val != q.Val {
        return false
    }
    return isSameTree(p.Left, q.Left) && isSameTree(p.Right, q.Right)
}

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function isSameTree(p: TreeNode | null, q: TreeNode | null): boolean {
    if (p == null && q == null) {
        return true;
    }
    if (p == null || q == null || p.val !== q.val) {
        return false;
    }
    return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
}

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {boolean}
 */
var isSameTree = function (p, q) {
    if (!p && !q) return true;
    if (p && q) {
        return (
            p.val === q.val &&
            isSameTree(p.left, q.left) &&
            isSameTree(p.right, q.right)
        );
    }
    return false;
};

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($val = 0, $left = null, $right = null) {
 *         $this->val = $val;
 *         $this->left = $left;
 *         $this->right = $right;
 *     }
 * }
 */
class Solution {
    /**
     * @param TreeNode $p
     * @param TreeNode $q
     * @return Boolean
     */
    function isSameTree($p, $q) {
        if ($p == Null && $q == Null) {
            return true;
        }
        if ($p == Null || $q == Null) {
            return false;
        }
        if ($p->val != $q->val) {
            return false;
        }
        return $this->isSameTree($p->left, $q->left) && $this->isSameTree($p->right, $q->right);
    }
}

// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
    fn dfs(p: &Option<Rc<RefCell<TreeNode>>>, q: &Option<Rc<RefCell<TreeNode>>>) -> bool {
        if p.is_none() && q.is_none() {
            return true;
        }
        if p.is_none() || q.is_none() {
            return false;
        }
        let r1 = p.as_ref().unwrap().borrow();
        let r2 = q.as_ref().unwrap().borrow();
        r1.val == r2.val && Self::dfs(&r1.left, &r2.left) && Self::dfs(&r1.right, &r2.right)
    }

    pub fn is_same_tree(
        p: Option<Rc<RefCell<TreeNode>>>,
        q: Option<Rc<RefCell<TreeNode>>>,
    ) -> bool {
        Self::dfs(&p, &q)
    }
}

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