Combination Sum IV

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations this add up t o a positive integer target.

Example:

nums = [1, 2, 3]target7.

Follow up:
What if negative numbers is allowed in the given array?
How does does it change the problem?
What limitation we need to add to the question to allow negative numbers?

Analyse:for every number I from 1 ... target, we check the numbers num in nums, if I >= num, we seperate i to num an D I-num, and compute how many ways i-num is consisted. That's to say, dp[i] + = Dp[i-num].

Runtime:4ms.

1 classSolution {2  Public:3     intCOMBINATIONSUM4 (vector<int>& Nums,inttarget) {4vector<int> dp (target +1,0);5         6dp[0] =1;7          for(inti =1; I <= target; i++) {8              for(Auto num:nums) {9                 if(I >=num)TenDp[i] + = dp[i-num]; One             } A         } -         returnDp[target]; -     } the};

Combination Sum IV