Climbing Stairs Problem in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the base case for 1 stair.

DSA Go

func climbStairs(n int) int {
    if n == 1 {
        return [1]
    }
    return 0
}

Drag options to blanks, or click blank then click option'

A1

B0

Cn

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 instead of 1 for the base case.

Returning n which is unnecessary here.

When there is only 1 stair, there is exactly 1 way to climb it.

2fill in blank

medium

Complete the code to return the base case for 2 stairs.

DSA Go

func climbStairs(n int) int {
    if n == 1 {
        return 1
    }
    if n == 2 {
        return [1]
    }
    return 0
}

Drag options to blanks, or click blank then click option'

A2

B1

C3

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 1 instead of 2 for the base case of 2 stairs.

Returning n which is 2 but not explaining the reasoning.

For 2 stairs, you can climb either 1 step + 1 step or 2 steps at once, so 2 ways.

3fill in blank

hard

Fix the error in the recursive return statement to calculate ways correctly.

DSA Go

func climbStairs(n int) int {
    if n == 1 {
        return 1
    }
    if n == 2 {
        return 2
    }
    return climbStairs(n [1] 1) + climbStairs(n - 2)
}

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of - causing syntax error or wrong logic.

Using * or / which do not make sense here.

We subtract 1 from n to get the previous step count, then add ways from n-2 steps.

4fill in blank

hard

Fill both blanks to create a map of stairs to ways using a loop.

DSA Go

func climbStairs(n int) int {
    ways := make(map[int]int)
    ways[1] = 1
    ways[2] = 2
    for i := 3; i <= n; i++ {
        ways[i] = ways[i [1] 1] + ways[i [2] 2]
    }
    return ways[n]
}

Drag options to blanks, or click blank then click option'

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + or * instead of - inside the map keys.

Using division which is invalid here.

We subtract 1 and 2 from i to get previous counts and sum their ways.

5fill in blank

hard

Fill all three blanks to create a slice and fill it with ways to climb stairs.

DSA Go

func climbStairs(n int) int {
    dp := make([]int, n+1)
    dp[1] = 1
    dp[2] = 2
    for i := 3; i <= n; i++ {
        dp[i] = dp[i [1] 1] [2] dp[i [3] 2]
    }
    return dp[n]
}

Drag options to blanks, or click blank then click option'

A-

B+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of addition.

Using addition inside indices instead of subtraction.

We subtract 1 and 2 from i to get previous dp values and add them to get current ways.

Practice

1. What does the Climbing Stairs problem ask you to find?
Given n steps, how many distinct ways can you climb to the top if you can take 1 or 2 steps at a time?

easy

A. The total number of distinct ways to reach the top

B. The minimum number of steps to reach the top

C. The maximum number of steps you can take at once

D. The number of steps you skip

Solution

1. Step 1: Understand the problem statement

   The problem asks for the count of different ways to climb to the top by taking 1 or 2 steps at a time.

2. Step 2: Identify what is being counted

   We count all possible sequences of 1-step and 2-step moves that sum to n steps.

3. Final Answer:

   The total number of distinct ways to reach the top -> Option A

4. Quick Check:

   Counting sequences of 1 or 2 steps = total ways [OK]

Hint: Count sequences of 1 or 2 steps summing to n [OK]

Common Mistakes:

• Confusing number of ways with minimum steps
• Thinking about maximum steps allowed
• Counting skipped steps instead of ways

2. Which Go function signature correctly represents a function to solve the Climbing Stairs problem for n steps?

easy

A. func climbStairs(n int) bool

B. func climbStairs(n string) string

C. func climbStairs() int

D. func climbStairs(n int) int

Solution

1. Step 1: Identify input and output types

   The input is the number of steps (integer), output is the count of ways (integer).

2. Step 2: Match function signature

   Only func climbStairs(n int) int matches input int and output int.

3. Final Answer:

   func climbStairs(n int) int -> Option D

4. Quick Check:

   Input int, output int = correct signature [OK]

Hint: Input and output both must be int for steps and ways [OK]

Common Mistakes:

• Using string instead of int for steps
• Missing input parameter
• Returning bool instead of int

3. What is the output of this Go code for n = 4?

func climbStairs(n int) int {
    if n <= 2 {
        return n
    }
    a, b := 1, 2
    for i := 3; i <= n; i++ {
        a, b = b, a+b
    }
    return b
}

fmt.Println(climbStairs(4))

medium

A. 7

B. 6

C. 5

D. 4

Solution

1. Step 1: Trace initial values and loop

   Start with a=1, b=2. Loop i=3 to 4:
   i=3: a=2, b=3
   i=4: a=3, b=5

2. Step 2: Return final value

   Return b=5 after loop ends.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   Ways for 4 steps = 5 [OK]

Hint: Use Fibonacci-like addition for steps count [OK]

Common Mistakes:

• Returning a instead of b
• Off-by-one error in loop range
• Incorrect initial values

4. Find the error in this Go code for climbing stairs:

func climbStairs(n int) int {
    if n == 1 {
        return 1
    }
    a, b := 1, 2
    for i := 2; i <= n; i++ {
        a, b = b, a+b
    }
    return b
}

medium

A. Return statement should return a instead of b

B. Loop starts at wrong index causing extra iteration

C. Initial values of a and b are incorrect

D. Missing base case for n == 2

Solution

1. Step 1: Analyze loop start and iterations

   Loop starts at i=2 but initial values already cover steps 1 and 2, causing one extra iteration.

2. Step 2: Correct loop start

   Loop should start at i=3 to avoid counting extra ways.

3. Final Answer:

   Loop starts at wrong index causing extra iteration -> Option B

4. Quick Check:

   Loop index off by one causes wrong count [OK]

Hint: Start loop at 3 when initial values cover steps 1 and 2 [OK]

Common Mistakes:

• Starting loop at 2 instead of 3
• Changing initial values incorrectly
• Returning wrong variable

5. You want to find the number of ways to climb 10 steps but can take 1, 2, or 3 steps at a time. How would you modify the climbing stairs approach?

hard

A. Use dynamic programming with dp[i] = dp[i-1] + dp[i-2] + dp[i-3]

B. Use the same formula dp[i] = dp[i-1] + dp[i-2]

C. Only count ways taking 3 steps at a time

D. Multiply the number of ways for 1 and 2 steps

Solution

1. Step 1: Understand the new step options

   Now you can take 1, 2, or 3 steps at a time, so ways to reach step i depend on previous 3 steps.

2. Step 2: Formulate recurrence relation

   Number of ways dp[i] = dp[i-1] + dp[i-2] + dp[i-3] to include all possibilities.

3. Final Answer:

   Use dynamic programming with dp[i] = dp[i-1] + dp[i-2] + dp[i-3] -> Option A

4. Quick Check:

   Include all step sizes in sum for dp [OK]

Hint: Sum ways from last 3 steps for 1,2,3 step moves [OK]

Common Mistakes:

• Using old formula for only 1 or 2 steps
• Ignoring 3-step moves
• Multiplying counts instead of adding