dp of size target + 1 with all elements set to 0.nums.target - 1 down to the number itself.dp[j] is not zero (indicating a subsequence of length dp[j] sums up to j), and j + nums[i] is less than or equal to target, update dp[j + nums[i]] to be the maximum of its current value and dp[j] + 1.dp[target] is zero, return -1, indicating no subsequence sums up to target. Otherwise, return dp[target].