FilesExpand file tree

 master

/

combinations.java

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

49 lines (42 loc) · 1.33 KB

 master

/

combinations.java

Copy path

Top

File metadata and controls

• Code
• Blame

49 lines (42 loc) · 1.33 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

public class Solution {

/**

* @param n: Given the range of numbers

* @param k: Given the numbers of combinations

* @return: All the combinations of k numbers out of 1..n

*/

public List<List<Integer>> combine(int n, int k) {

// write your code here

List<List<Integer>> res = new ArrayList<List<Integer>>();

if (n <= 0 || k == 0) {

return res;

}

int[] nums = new int[n];

for (int i = 0; i < nums.length; i++) {

nums[i] = i + 1;

}

List<Integer> tempList = new ArrayList<Integer>();

// 1 2 3 4

for (int i = 0; i <= n - k; i++) {

tempList.add(nums[i]);

helper(res, tempList, nums, k, i + 1);

tempList.remove(tempList.size() - 1);

}

return res;

}

public void helper(List<List<Integer>> res, List<Integer> tempList, int[] nums,

int len, int index) {

if (tempList.size() == len) {

// valid match.

res.add(new ArrayList<Integer>(tempList));

return;

}

if (index == nums.length) {

return;

}

for (int i = index; i < nums.length; i++) {

tempList.add(nums[i]);

helper(res, tempList, nums, len, i + 1);

tempList.remove(tempList.size() - 1);

}

}

}