1. Description

Given a set of candidate numbers (C) (without duplicates) 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.

2. Runtime Distribution

3. Submission Details

4. Example

given candidate set [2, 3, 6, 7] and target 7,
A solution set is:
[
[7],
[2, 2, 3]
]

5. Code

public List<List<Integer>> combinationSum(int[] candidates, int target) {
    List<List<Integer>> results = new ArrayList<List<Integer>>();
    if (candidates == null || candidates.length == 0 || target <= 0) {
        return results;
    }
    LinkedList<Integer> records = new LinkedList<Integer>();
    dfs(candidates, 0, records, results, target);
    return results;
}

private void dfs(int[] candidates, int start, LinkedList<Integer> records, List<List<Integer>> results,
        int target) {
    if (target == 0) {
        results.add(new LinkedList<Integer>(records));
    }
    if (target <= 0) {
        return;
    }
    for (int i = start; i < candidates.length; i++) {
        records.offer(candidates[i]);
        dfs(candidates, i, records, results, target - candidates[i]);
        records.pollLast();
    }
}

6.Test

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

public class LeetCode0039 {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> results = new ArrayList<List<Integer>>();
        if (candidates == null || candidates.length == 0 || target <= 0) {
            return results;
        }
        LinkedList<Integer> records = new LinkedList<Integer>();
        dfs(candidates, 0, records, results, target);
        return results;
    }

    private void dfs(int[] candidates, int start, LinkedList<Integer> records, List<List<Integer>> results,
            int target) {
        if (target == 0) {
            results.add(new LinkedList<Integer>(records));
        }
        if (target <= 0) {
            return;
        }
        for (int i = start; i < candidates.length; i++) {
            records.offer(candidates[i]);
            dfs(candidates, i, records, results, target - candidates[i]);
            records.pollLast();
        }
    }

    public static void main(String[] args) {
        LeetCode0039 leetcode = new LeetCode0039();
        int[] candidates = { 2, 3, 6, 7 };
        List<List<Integer>> results = leetcode.combinationSum(candidates, 7);
        for (int i = 0; i < results.size(); i++) {
            for (int j = 0; j < results.get(i).size(); j++) {
                System.out.print(results.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
}