Add solution

dynamic-programming/coin-combinations-i/README.md

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+# Coin Combinations I
+
+Problem page: <https://cses.fi/problemset/task/1635/>

dynamic-programming/coin-combinations-i/main.cpp

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+#include <iostream>
+
+#define MOD (int)1e9 + 7
+
+using namespace std;
+
+int main(){
+    int n{}, x{};
+    cin >> n >> x;
+
+    int coins[n];
+    for (auto &c : coins){
+        cin >> c;
+    }
+
+    int memo[x+1];
+    memo[0] = 1;
+
+    for (int i = 1; i <= x; i++){
+        memo[i] = 0;
+        for (auto c : coins){
+            if (i-c >= 0){
+                memo[i] += memo[i-c];
+                memo[i] %= MOD;
+            }
+        }
+    }
+
+    cout << memo[x] << "\n";
+
+    return 0;
+}