I was doing this Problem on codeforces. It was a dynamic programming question and I am fairly new to dynamic programming.

I wrote a code whose main part is below

n,m,b,mod = li()
a = li()
dp = [[0 for i in range(b+1)] for j in range(m+1)] 
dp[0][0]=1
for i in range(n):
    for j in range(1,m+1):
        for k in range(b+1):
            if k-a[i]>=0:
                dp[j][k]+=dp[j-1][k-a[i]]
ans = 0
for j in range(b+1):
    ans+= dp[m][j]
print(ans%mod)

This was giving the correct output. But when I move the first loop to the end, then it gives the wrong answer.

for j in range(1,m+1):
    for k in range(b+1):
        for i in range(n):
            if k-a[i]>=0:
                dp[j][k]+=dp[j-1][k-a[i]]

The above code is giving incorrect output. Can anybody help me in understanding why does the loop orientation matters in this case.