Program to find number of coins needed to make the changes in Python


Suppose we have coins of different denominations (1,5,10,25) and a total amount of money amount. We have to define one function to compute the fewest number of coins that we need to make up that amount. So if the input is 64, the output is 7. This is formed using 25 + 25 + 10 + 1 + 1 + 1 + 1 = 64.

To solve this, we will follow these steps −

  • if amount = 0, then return 0
  • if minimum of coins array > amount, then return -1
  • define one array called dp, of size amount + 1, and fill this with -1
  • for i in range coins array
    • if i > length of dp – 1, then skip the next part, go for the next iteration
    • dp[i] := 1
    • for j in range i + 1 to amount
      • if dp[j – 1] = -1, then skip the next part, go for the next iteration
      • otherwise if dp[j] = -1, then dp[j] := dp[j - i] + 1
      • otherwise dp[j] := minimum of dp[j] and dp[j – i] + 1
  • return dp[amount]

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution(object):
   def coinChange(self, amount):
      coins = [1,5,10,25]
      if amount == 0 :
         return 0
      if min(coins) > amount:
         return -1
      dp = [-1 for i in range(0, amount + 1)]
      for i in coins:
         if i > len(dp) - 1:
            continue
         dp[i] = 1
         for j in range(i + 1, amount + 1):
            if dp[j - i] == -1:
               continue
            elif dp[j] == -1:
               dp[j] = dp[j - i] + 1
            else:
               dp[j] = min(dp[j], dp[j - i] + 1)
      return dp[amount]
ob1 = Solution()
print(ob1.coinChange(64))

Input

64

Output

7

Updated on: 19-Oct-2020

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