Leetcode 377. Combination Sum IV (Medium) (cpp)

Leetcode 377. Combination Sum IV (Medium) (cpp)

Tag: Dynamic Programming

Difficulty: Medium

/*

377. Combination Sum IV (Medium)

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?

*/
class Solution {
public:
	int combinationSum4(vector& nums, int target) {
		vector table(target + 1);
		table[0] = 1;
		for (int i = 1; i <= target; i++) {
			for (int j : nums) {
				if (i - j >= 0) table[i] += table[i - j]; 
			}
		}
		return table.back();
	}
};