BackTracking
BackTracking (DFS)
39. 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.
- 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 class Solution { public List<List<Integer>> combinationSum(int[] candidates, int target) { List<List<Integer>> res = new ArrayList<>(); List<Integer> member = new ArrayList<Integer>(); helper(res, member, candidates, target, 0); return res; } public void helper(List<List<Integer>> res, List<Integer> member, int[] candidates, int target, int start){ if(target < 0) return; else if(target == 0){ res.add(new ArrayList<Integer>(member)); //member is address return; } else{ for(int i = start; i < candidates.length; i++){ member.add(candidates[i]); helper(res, member, candidates, target - candidates[i], i ); member.remove(member.size() - 1); //make member empty! } } } }
40. 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.
- 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 class Solution { public List<List<Integer>> combinationSum2(int[] candidates, int target) { List<List<Integer>> res = new ArrayList<>(); List<Integer> member = new ArrayList<>(); Arrays.sort(candidates); boolean visit[] = new boolean[candidates.length]; helper(res, member, visit, candidates, target, 0); return res; } public void helper(List<List<Integer>> res, List<Integer> member ,boolean[] visit, int[] candidates , int target ,int deep){ if(target < 0) return ; else if(target == 0){ res.add(new ArrayList<Integer>(member)); return; } else{ for(int i = deep; i < candidates.length; i++){ if(!visit[i]){ if (i > 0 && candidates[i] == candidates[i-1] && visit[i-1]==false) continue; member.add(candidates[i]); visit[i] = true; helper(res, member, visit, candidates, target - candidates[i], i); visit[i] = false; member.remove(member.size() - 1); } } } } }