Coin change problem - Dynamic programming
Problem:
Given a value N, if we want to make change for N cents, and we have infinite supply of each of S = { S1, S2, .. , Sm} valued coins, how many ways can we make the change? The order of coins doesn’t matter.
For example, for N = 4 and S = {1,2,3}, there are four solutions: {1,1,1,1},{1,1,2},{2,2},{1,3}. So output should be 4. For N = 10 and S = {2, 5, 3, 6}, there are five solutions: {2,2,2,2,2}, {2,2,3,3}, {2,2,6}, {2,3,5} and {5,5}. So the output should be 5.
Solution:
/* Dynamic Programming Java implementation of Coin Change problem */ import java.util.Arrays; class CoinChange { static long countWays( int S[], int m, int n) { //Time complexity of this function: O(mn) //Space Complexity of this function: O(n) // table[i] will be storing the number of solutions // for value i. We need n+1 rows as the table is // constructed in bottom up manner using the base // case (n = 0) long [] table = new long [n+ 1 ]; // Initialize all table values as 0 Arrays.fill(table, 0 ); //O(n) // Base case (If given value is 0) table[ 0 ] = 1 ; // Pick all coins one by one and update the table[] // values after the index greater than or equal to // the value of the picked coin for ( int i= 0 ; i<m; i++) for ( int j=S[i]; j<=n; j++) table[j] += table[j-S[i]]; return table[n]; } // Driver Function to test above function public static void main(String args[]) { int arr[] = { 1 , 2 , 3 }; int m = arr.length; int n = 4 ; System.out.println(countWays(arr, m, n)); } } |
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