HackerRank The Coin Change Problem

long grid[50][260];
long solve(int idx,int n,vector<long> & coins){
    if((int) coins.size() == idx or n == 0){
        return  n == 0;
    }
    if(grid[idx][n] != -1){
        return grid[idx][n];
    }
    long res = 0;
    for(int i = 0;i <= n / coins[idx]; i++){
        res += solve(idx + 1,n - (coins[idx] * i),coins);
    }
    return grid[idx][n] = res;
}
long getWays(int n, vector<long> &c) {
    memset(grid,-1,sizeof(grid));
    return solve(0,n,c);
}