Update coin_change_2.cpp

Author: caba5

cpp/neetcode_150/14_2-d_dynamic_programming/coin_change_2.cpp

@@ -7,7 +7,7 @@
     Time: O(m x n)
     Space: O(m x n)
 */
-
+/*
 class Solution {
 public:
     int change(int amount, vector<int>& coins) {
@@ -37,3 +37,47 @@ class Solution {
         return dp[{i, sum}];
     }
 };
+*/
+// DP programming solution using a matrix
+/*
+class Solution {
+public:
+    int change(int amount, vector<int>& coins) {
+        vector<vector<int>> DP(coins.size() + 1, vector<int>(amount+1));
+        
+        for (int i = 0; i < coins.size() + 1; ++i)
+            DP[i][0] = 1;
+
+        for (int i = 1; i <= coins.size(); ++i){
+            for (int j = 0; j <= amount; ++j){
+                DP[i][j] = DP[i-1][j];
+                if (j - coins[i-1] >= 0)
+                    DP[i][j] +=  DP[i][j - coins[i-1]];
+            }
+        }
+
+        return DP[coins.size()][amount];
+    }
+};
+// O(m) space solution
+*/
+class Solution {
+public:
+    int change(int amount, vector<int>& coins) {
+        vector<int> prev(amount+1);
+        vector<int> curr(amount+1);
+
+        prev[0] = 1;
+
+        for (int i = 0; i < coins.size(); ++i){
+            for (int j = 0; j <= amount; ++j){
+                curr[j] = prev[j];
+                if (j - coins[i] >= 0)
+                    curr[j] +=  curr[j - coins[i]];
+            }
+            prev = curr;
+        }
+
+        return curr[amount];
+    }
+};