Leetcode Combinations-----java

Given-integers n and K, return all possible combinations of K numbers out of 1 ... n.

For example,
If N = 4 and k = 2, a solution is:

[  [2,4],  [3,4], [  2,3],  [up],  [1,3],  [1,4],]

All results of C (k,n) are obtained.

It is simpler and more efficient to use backtracking (backtracking) to explain the problem.

 Public classSolution { PublicList<list<integer>> Combine (intNintk) {List<List<Integer>> res =NewArraylist<list<integer>>(); Con (N,k,0,0,res,New int[K]); returnRes; }     Public voidCon (intNintKintNumintstart,list<list<integer>> Res,int[] ans) {        if(num = =k) {ArrayList<Integer> TT =NewArraylist<integer>();  for(inti = 0;i<k;i++) Tt.add (Ans[i]);            Res.add (TT); return ; }         for(inti = start;i<n;i++) {Ans[num]= I+1; Con (N,k,num+1,i+1, Res,ans); }        return ;}}

One thing that can be fixed is that the for loop in con is changed to

for (int i = start;i<=n-(k-num); i++)

This can further increase the speed. Also, setting res as a global variable would look good in code.

Leetcode Combinations-----java