377. Combination Sum IV

377. Combination Sum IV

• 題目描述：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.

• 題目大意：給定一個數組，一個target，問數組中有多少組合，使它們的和爲目標數target

• 代碼

  package DP;
  
  import java.util.Arrays;
  
  /**
  * @author OovEver
  * 2018/1/3 16:11
  */
  public class LeetCode377 {
    public static int combinationSum4(int[] nums, int target) {
        Arrays.sort(nums);
  //        dp[i]表示，以i爲target有多少種組成情況
        int[] dp = new int[target + 1];
        for(int i=1;i<target+1;i++) {
            for (int num : nums) {
                if (i < num) {
                    break;
                }
                if (i == num) {
                    dp[i] += 1;
                } else {
                    dp[i] += dp[i - num];
                }
            }
        }
        return dp[target];
    }
  }