kind of a solution for https://cses.fi/problemset/task/1636/

a.cpp

#include <stdio.h>

#define M 101
#define N 1000001
#define mod 1000000007

int n,x;
int dp[N][M]={0};
int vec[M];

int main() {

    scanf("%d%d",&n,&x);
    for(int i=0;i<n;i++) dp[0][i]=1;
    for(int i=0;i<n;i++) scanf("%d",&vec[i]);

    for(int i=1;i<=x;i++) {
        for(int j=0;j<n;j++) {
            long long int l = dp[i][j];
            if(i>=vec[j]) l = (l+dp[i-vec[j]][j]);
            if(j>0) l = (l+dp[i][j-1]);
            dp[i][j] = (l%mod);
        }
    }

    printf("%d\n",dp[x][n-1]);

    return 0;
}