Leetcode 377: Combination Sum IV
Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.
Example:
nums = [1, 2, 3] target = 4 The possible combination ways are: (1, 1, 1, 1) (1, 1, 2) (1, 2, 1) (1, 3) (2, 1, 1) (2, 2) (3, 1) Note that different sequences are counted as different combinations. Therefore the output is 7.
Follow up:
What if negative numbers are allowed in the given array?
How does it change the problem?
What limitation we need to add to the question to allow negative numbers?
1 public class Solution { 2 public int CombinationSum4(int[] nums, int target) { 3 if (target < 0) return 0; 4 5 var dp = new int[target + 1]; 6 dp[0] = 1; 7 8 for (int i = 1; i <= target; i++) 9 { 10 for (int j = 0; j < nums.Length; j++) 11 { 12 if (i - nums[j] >= 0) 13 { 14 dp[i] += dp[i - nums[j]]; 15 } 16 } 17 } 18 19 return dp[target]; 20 } 21 }