求问 dp 后缀和优化

f[0][n][0] = 1;
for (int i = 1;i <= n;i++)
	for (int j = n;j >= 1;j--)
		for (int k = j;k <= sum[i];k++)
			for (int o = j;o <= n;o++)
				f[i][j][k] = mod(f[i][j][k]+f[i-1][o][k-j]);
int ans = 0;
for (int i = n;i >= 1;i--)
	ans = mod(ans+f[n][i][s]);
printf("%d\n",ans);

for (int i = 1;i <= n;i++) f[0][i][0] = 1;
for (int i = 1;i <= n;i++)
	for (int j = n;j >= 1;j--)
		for (int k = j;k <= sum[i];k++)
			f[i][j][k] = mod(f[i][j+1][k]+f[i-1][j][k-1]);
printf("%d\n",f[n][1][s]);