[Solved] The following code attempts to solve the coin change minimum coins problem.... Identify the line containing the subtle bug that causes incorrect results or infinite recursion for amount=0. | Dynamic Programming: Knapsack

Dynamic Programming: Knapsack - Coin Change (Minimum Coins)

The following code attempts to solve the coin change minimum coins problem. Identify the line containing the subtle bug that causes incorrect results or infinite recursion for amount=0.

def coinChange(coins, amount):
    def dfs(rem):
        if rem == 0:
            return 0
        res = float('inf')
        for coin in coins:
            if rem - coin >= 0:
                res = min(res, 1 + dfs(rem - coin))
        return res
    ans = dfs(amount)
    return ans if ans != float('inf') else -1

ALine 3: Missing base case for rem < 0

BLine 6: Missing check for rem == 0 before recursion

CLine 9: Returning res without checking if res is still infinity

DLine 7: Incorrect condition rem - coin >= 0 instead of rem >= coin

Step-by-Step Solution

Solution:

Step 1: Analyze base cases in recursion
Code handles rem == 0 but lacks base case for rem < 0, but since rem - coin >= 0 check prevents negative rem, no infinite recursion occurs.
Step 2: Check return value correctness
Returning res directly without checking if res is still infinity can cause incorrect results when no valid coin combination exists.
Final Answer:
Option C -> Option C
Quick Check:
Must check if res is infinity before returning to handle no solution cases correctly [OK]

Quick Trick: Check if result is infinity before returning in recursion [OK]

Common Mistakes:

MISTAKES

Forgetting to handle no solution case
Assuming rem == 0 base case suffices

Trap Explanation:

PITFALL

Candidates often miss that returning infinity without check leads to wrong answers when no combination exists.

Interviewer Note:

CONTEXT

Tests candidate's attention to recursion return values and edge cases.

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More Dynamic Programming: Knapsack Quizzes

The following code attempts to solve the coin change minimum coins problem. Identify the line containing the subtle bug that causes incorrect results or infinite recursion for amount=0.

Step 1: Analyze base cases in recursion

Step 2: Check return value correctness

Final Answer:

Quick Check:

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