Combination SumIII; BackTracking; Array;

最新推荐文章于 2021-02-19 09:59:25 发布

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最新推荐文章于 2021-02-19 09:59:25 发布

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原文链接：http://www.cnblogs.com/5683yue/p/5229563.html

本文详细解析了组合求和问题的递归算法实现，并通过具体示例代码展示了如何找到所有可能的有效组合。针对参数为列表的情况，特别强调了在递归过程中如何避免重复元素的问题。

Note that when you put the list to be the parameter, and each time you do the recursion, you add element into the list, you need to remove the former added elements in the previous combination.

Code:

public class Solution {
    public List<List<Integer>> combinationSum3(int k, int n) {
        List<List<Integer>> ret = new ArrayList<>();
        List<Integer> list = new ArrayList<>();
        combination(list, ret, k, n, 0, 1);
        return ret;
    }
    
    public void combination(List<Integer> list, List<List<Integer>> ret, int k, int remain, 
                int last, int index){
        if(remain < last+1) return;
        if(index == k){
            if(remain > 9) return;
            list.add(remain);
            ret.add(new ArrayList(list));
            list.remove(list.size()-1);
            return;
        }
        for(int i = last+1; i <= remain && i <= 9; i++){
                //if(!status) break;
                if(index == 1) list = new ArrayList<>();
                list.add(i);
                combination(list, ret, k, remain-i, i, index+1);
                list.remove(list.size()-1);
        }
    }
    
}