leetcode coin change problem doesn't give correct result

Question

I'm writing codes to solve this problem, below are my codes, somehow I see the result is correct till the end of the for loop, but after the function returns it doesn't carry out the correct result value, see below the log print, anybody could help with it? Thanks!

https://leetcode.com/problems/coin-change/

"""
sort the coins to start with coin that has largest value;
then loop through possible number of that coins we could put, 
and use dfs to go through other possible coin types
"""
def coinChange(self, coins, amount):
    # write your code here
    coins.sort()
    coins=coins[::-1]

    n=len(coins)
    res=100000000000000



    def getcom(i, coins, amount,count, res):

        if amount==0:
            res=min(res, count)
            print("res: ", res)


        if i==n:
            return

        coin=coins[i]
        print("coin:", coins[i])
        k=amount//coin
        print("k:", k)
        for j in range(k, -1, -1):
            if count+j>res:
                break
            getcom(i+1, coins, amount-k*coin, count+k, res)

    getcom(0,coins, amount, 0,res)        
    return res

testcase:Input: coins = [1, 2, 5], amount = 11
should Output: 3

Explanation: 11 = 5 + 5 + 1

my stdout
coin: 5
k: 2
coin: 2
k: 0
coin: 1
k: 1
res:  3
res:  3
coin: 2
k: 0
coin: 1
k: 1
res:  3
res:  3
coin: 2
k: 0
coin: 1
k: 1
res:  3
res:  3

----------
my output: 100000000000000

Have you done any debugging? I would recommend reading https://ericlippert.com/2014/03/05/how-to-debug-small-programs/. — AMC, Mar 26 '20 at 01:04

score 0 · Answer 1 · answered Mar 25 '20 at 21:54

res is being modified in the method calls but never returned.

The result from your recursive computation is not being passed back up the call stack. You need to add some return statements.

"""
sort the coins to start with coin that has largest value;
then loop through possible number of that coins we could put, 
and use dfs to go through other possible coin types
"""
def coinChange(coins, amount):
    # write your code here
    coins.sort()
    coins=coins[::-1]

    n=len(coins)
    res=100000000000000



    def getcom(i, coins, amount,count, res):
        #nonlocal res
        if amount==0:
            res=min(res, count)
            print("res: ", res)


        if i==n:
            return res

        coin=coins[i]
        print("coin:", coins[i])
        k=amount//coin
        print("k:", k)
        for j in range(k, -1, -1):
            if count+j>res:
                break
            return getcom(i+1, coins, amount-k*coin, count+k, res)

    res = getcom(0,coins, amount, 0,res)
    return res

print(coinChange([1,2,5], 11))

Output:

coin: 5
k: 2
coin: 2
k: 0
coin: 1
k: 1
res:  3
3

leetcode coin change problem doesn't give correct result

Explanation: 11 = 5 + 5 + 1

1 Answers1