Leetcode 377 Combination Sum IV Java

问题：
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.

解答

public class L377 {
	public int combinationSum4(int[] nums, int target) {
		//这个利用动态规划的思想
		int [] dp = new int [target + 1];
		dp[0] = 1;
		for(int i = 1; i < dp.length; i ++) {
			for(int j = 0; j < nums.length; j ++) {
				if(i - nums[j] >= 0) {
					dp[i] += dp[i - nums[j]];
				}
			}
		}
		return dp[target];
	}
}