Check if Two Trees are Symmetric in DSA Go - Build from Scratch

Check if Two Trees are Symmetric

📖 Scenario: You are working with two simple binary trees representing family trees. You want to check if these two trees are mirror images of each other, meaning they are symmetric.

🎯 Goal: Build a Go program that creates two binary trees, sets a helper variable, writes a function to check if the trees are symmetric, and prints the result.

📋 What You'll Learn

Create two binary trees using the TreeNode struct with exact values

Create a helper variable result of type bool

Write a function isSymmetric that checks if two trees are symmetric

Print the value of result

💡 Why This Matters

🌍 Real World

Checking if two trees are symmetric is useful in comparing hierarchical data structures like family trees, organizational charts, or XML/JSON data.

💼 Career

Understanding tree symmetry helps in software development roles involving data structure manipulation, algorithm design, and problem-solving.

1

Create two binary trees

Create two binary trees using the TreeNode struct with these exact values: root1 with value 1, left child 2, right child 3; and root2 with value 1, left child 3, right child 2.

DSA Go

package main

import "fmt"

type TreeNode struct {
    Val   int
    Left  *TreeNode
    Right *TreeNode
}

func main() {
    // Create root1 tree
    // Your code here
}

Hint

Use the &TreeNode{Val: value} syntax to create nodes and assign left and right children.

2

Create a helper variable

Create a boolean variable called result and set it to false inside the main function.

DSA Go

package main

import "fmt"

type TreeNode struct {
    Val   int
    Left  *TreeNode
    Right *TreeNode
}

func main() {
    root1 := &TreeNode{Val: 1}
    root1.Left = &TreeNode{Val: 2}
    root1.Right = &TreeNode{Val: 3}

    root2 := &TreeNode{Val: 1}
    root2.Left = &TreeNode{Val: 3}
    root2.Right = &TreeNode{Val: 2}

    // Create a boolean variable result and set it to false
    // Your code here
}

Hint

Use result := false to create and initialize the boolean variable.

3

Write the function to check symmetry

Write a function called isSymmetric that takes two pointers to TreeNode named t1 and t2 and returns a bool. It should return true if both trees are symmetric (mirror images), otherwise false. Use recursion to compare nodes. Then, inside main, set result to the call isSymmetric(root1, root2).

DSA Go

func isSymmetric(t1 *TreeNode, t2 *TreeNode) bool {
    if t1 == nil && t2 == nil {
        return true
    }
    if t1 == nil || t2 == nil {
        return false
    }
    if t1.Val != t2.Val {
        return false
    }
    return isSymmetric(t1.Left, t2.Right) && isSymmetric(t1.Right, t2.Left)
    result = isSymmetric(root1, root2)

Hint

Check if both nodes are nil, then if one is nil, then if values differ. Recursively check left of one with right of other and vice versa.

4

Print the result

Print the value of the boolean variable result inside the main function.

DSA Go

Hint

Use fmt.Println(result) to print the boolean value.

Practice

1. What does it mean for two binary trees to be symmetric?

easy

A. They are mirror images of each other around their center.

B. They have the same number of nodes.

C. They have the same root value only.

D. They have identical left subtrees only.

Solution

1. Step 1: Understand symmetry in trees

   Two trees are symmetric if one is the mirror reflection of the other around the center.

2. Step 2: Compare structure and node values

   Both structure and node values must match in a mirrored way for symmetry.

3. Final Answer:

   They are mirror images of each other around their center. -> Option A

4. Quick Check:

   Symmetry means mirror image [OK]

Hint: Symmetric trees mirror each other exactly [OK]

Common Mistakes:

• Thinking same number of nodes means symmetric
• Only comparing root values
• Ignoring structure differences

2. Which Go function signature correctly represents a function to check if two trees are symmetric?

easy

A. func isSymmetric(t1 *TreeNode) bool

B. func isSymmetric(t1 TreeNode, t2 TreeNode) int

C. func isSymmetric(t1 *TreeNode, t2 *TreeNode) bool

D. func isSymmetric(t1 *TreeNode, t2 *TreeNode) string

Solution

1. Step 1: Identify correct parameter types

   Function should take pointers to TreeNode structs for both trees to compare.

2. Step 2: Identify correct return type

   Return type should be bool to indicate symmetric (true) or not (false).

3. Final Answer:

   func isSymmetric(t1 *TreeNode, t2 *TreeNode) bool -> Option C

4. Quick Check:

   Pointer params and bool return [OK]

Hint: Use pointers and bool return for tree comparison [OK]

Common Mistakes:

• Using value instead of pointer for trees
• Returning int or string instead of bool
• Missing one tree parameter

3. What will be the output of the following Go code snippet?

package main
import "fmt"

type TreeNode struct {
    Val int
    Left, Right *TreeNode
}

func isSymmetric(t1, t2 *TreeNode) bool {
    if t1 == nil && t2 == nil {
        return true
    }
    if t1 == nil || t2 == nil {
        return false
    }
    return t1.Val == t2.Val && isSymmetric(t1.Left, t2.Right) && isSymmetric(t1.Right, t2.Left)
}

func main() {
    root1 := &TreeNode{Val: 1, Left: &TreeNode{Val: 2}, Right: &TreeNode{Val: 2}}
    root2 := &TreeNode{Val: 1, Left: &TreeNode{Val: 2}, Right: &TreeNode{Val: 3}}
    fmt.Println(isSymmetric(root1, root2))
}

medium

A. true

B. false

C. Compilation error

D. Runtime panic

Solution

1. Step 1: Compare root nodes

   Both roots have value 1, so check children.

2. Step 2: Compare left and right subtrees

   Left subtree of root1 has value 2, right subtree of root2 has value 3, which differ.

3. Final Answer:

   false -> Option B

4. Quick Check:

   Different child values mean not symmetric [OK]

Hint: Check mirrored child values for symmetry [OK]

Common Mistakes:

• Assuming same root means symmetric
• Ignoring mismatch in child nodes
• Confusing symmetric with identical

4. Identify the bug in the following Go function that checks if two trees are symmetric:

func isSymmetric(t1, t2 *TreeNode) bool {
    if t1 == nil && t2 == nil {
        return true
    }
    if t1 == nil || t2 == nil {
        return false
    }
    return t1.Val == t2.Val && isSymmetric(t1.Left, t2.Left) && isSymmetric(t1.Right, t2.Right)
}

medium

A. The function does not check root node values.

B. The base case for nil nodes is missing.

C. The function should return int, not bool.

D. The recursive calls compare wrong child nodes for symmetry.

Solution

1. Step 1: Check recursive calls for symmetry

   Symmetry requires comparing left of one tree with right of the other, but code compares left with left and right with right.

2. Step 2: Identify correct recursive calls

   Correct calls should be isSymmetric(t1.Left, t2.Right) and isSymmetric(t1.Right, t2.Left).

3. Final Answer:

   The recursive calls compare wrong child nodes for symmetry. -> Option D

4. Quick Check:

   Mirror children must be compared [OK]

Hint: Compare left with right child for symmetry [OK]

Common Mistakes:

• Comparing left with left and right with right
• Missing nil base cases
• Returning wrong type

5. Given two binary trees, write a Go function to check if they are symmetric. Which approach correctly handles the edge case where one tree is nil and the other is not?

hard

A. Return false immediately if one tree is nil and the other is not.

B. Return true if one tree is nil and the other is not.

C. Ignore nil checks and compare node values only.

D. Return true if both trees have the same number of nodes.

Solution

1. Step 1: Handle nil tree edge cases

   If one tree is nil and the other is not, they cannot be symmetric, so return false immediately.

2. Step 2: Ensure correct base cases in recursion

   Only return true if both trees are nil at the same time, otherwise false.

3. Final Answer:

   Return false immediately if one tree is nil and the other is not. -> Option A

4. Quick Check:

   Nil mismatch means not symmetric [OK]

Hint: Check nil mismatch first to avoid errors [OK]

Common Mistakes:

• Returning true when one tree is nil
• Skipping nil checks causing runtime errors
• Comparing only node counts