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LeetCode 77:组合
2022-07-06 19:10:00 【斯沃福德】
链接
题目:
思路:回溯(无重复元素不可复选)
与子集类似,数据无重复,且(2,1)和(1,2)是一个结果,故不能复选;
子集问题中每一个节点都是子集,但组合问题中当元素个数到达k才将path放入res中!
注意:
集合问题中,给的是数组,for从0到n-1 ;组合问题给的n,for从1到n ;
Java实现:
class Solution {
List<List<Integer>> res=new LinkedList<>();
LinkedList<Integer> path=new LinkedList<>();
public List<List<Integer>> combine(int n, int k) {
dfs(n,k,1); // 注意start从1开始
return res;
}
void dfs(int n,int k,int start){
//终止条件,当元素个数为k则添加
if(path.size()==k){
res.add(new LinkedList(path));
}
for(int i=start;i<=n;i++){
//递归前做选择
path.add(i);
//递归
dfs(n,k,i+1);
//递归后撤销选择
path.removeLast();
}
}
}
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