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Combination Sum

2024-07-08 01:56:31   223人阅读

题目

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] 

方法

先对数组排序，使用递归选取元素，选择递归的条件。
    private void getCom(int[] candidates, int target, int start, List<Integer> subList, List<List<Integer>> list) {
        for (int i = start; i < candidates.length; i++) {
            List<Integer> newList = new ArrayList<Integer>(subList);
            if (target - candidates[i] == 0) {
                newList.add(candidates[i]);
                list.add(newList);
            } else if (target - candidates[i] > 0) {
                newList.add(candidates[i]);
                getCom(candidates, target - candidates[i], i, newList, list);
            } else {
                break;
            }
        }
    }
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        Arrays.sort(candidates);
        List<List<Integer>> list = new ArrayList<List<Integer>>();
        List<Integer> subList = new ArrayList<Integer>();
        getCom(candidates, target, 0, subList, list);
        return list;
    }


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