1.Combination Sum
Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.
The same repeated number may be chosen from C unlimited number of times.
Note:
- All numbers (including target) will be positive integers.
- Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
- The solution set must not contain duplicate combinations.
For example, given candidate set 2,3,6,7
and target 7
,
A solution set is:
[7]
[2, 2, 3]
public List<List<Integer>> combinationSum(int[] candidates, int target) {
List<List<Integer>> res=new ArrayList<List<Integer>>();
if(candidates==null||candidates.length==0)
return res;
Arrays.sort(candidates);
combinationSum(candidates, target,0,new ArrayList<Integer>(),res);
return res;
}
private static void combinationSum(int[] candidates, int target, int start, ArrayList<Integer> list,
List<List<Integer>> res) {
if(target==0){
res.add(list);
return;
}
for(int i=start;i<candidates.length;i++){
if(target-candidates[i]>=0){
ArrayList<Integer> tmp=(ArrayList<Integer>)list.clone();
int tmp_target=target-candidates[i];
tmp.add(candidates[i]);
combinationSum(candidates, tmp_target, i, tmp, res);
}
}
}</span>
2.
Combination Sum II
Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.
Each number in C may only be used once in the combination.
Note:
- All numbers (including target) will be positive integers.
- Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
- The solution set must not contain duplicate combinations.
For example, given candidate set 10,1,2,7,6,1,5
and target 8
,
A solution set is:
[1, 7]
[1, 2, 5]
[2, 6]
[1, 1, 6]
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
List<List<Integer>> res=new ArrayList<List<Integer>>();
if(candidates==null||candidates.length==0)
return res;
Arrays.sort(candidates);
combinationSum2(candidates,target,0,new ArrayList<Integer>(),res);
return res;
}
private static void combinationSum2(int[] candidates, int target, int start, ArrayList<Integer> arrayList,
List<List<Integer>> res) {
if(target==0){
res.add(arrayList);
return;
}
for(int i=start;i<candidates.length;i++){
if (i > start && candidates[i] == candidates[i-1]) continue;
if(target-candidates[i]>=0){
ArrayList<Integer> tmp=(ArrayList<Integer>)arrayList.clone();
int tmp_target=target-candidates[i];
tmp.add(candidates[i]);
combinationSum2(candidates, tmp_target, i+1, tmp, res);
}
}
}</span>
Combination Sum III
Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.
Ensure that numbers within the set are sorted in ascending order.
Example 1:
Input: k = 3, n = 7
Output:
[[1,2,4]]
Example 2:
Input: k = 3, n = 9
Output:
[[1,2,6], [1,3,5], [2,3,4]]
public List<List<Integer>> combinationSum3(int k, int n) { List<List<Integer>> res = new ArrayList<>(); Deque<Integer> tmp = new ArrayDeque<>(); if (n == 0 || k == 0 || n / k > 9) { return res; } helper(res, tmp, 1, k, n); return res; } private void helper(List<List<Integer>> res, Deque<Integer> tmp, int start, int k, int n) { if (0 == n && k == 0) { res.add(new ArrayList<>(tmp)); return; } for (int i = start; i <= 9; i++) { tmp.addLast(i); helper(res, tmp, i + 1, k - 1, n - i); tmp.removeLast(); } }</span>