[leetcode] problem 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?

Code

public int (int[] nums, int target) {
    int[] dp = new int[target + 1];
    dp[0] = 1;

    
    for (int i = 1; i <= target; i++) {
        for (int num : nums) {
            if (i >= num)
                dp[i] += dp[i - num];
        }
    }

    return dp[target];
}

[leetcode] problem 377 – combination sum iv

Example

Follow up

Code

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