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2024-08-12 13:38:32   212人阅读

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);                }                            }        }    }}

 

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