代码随想录day24

77. 组合

解题步骤：

1、确定回溯函数参数及返回值；

vector<vector<int>> result;

vector<int> path;

void backtracking (int n, int k, int startIndex)

2、确定回溯结束条件

　　单层路径大小为k

if (path.size() == k) {

result.push_back(path);

return;

}

3、确定单层逻辑

for (int i = startIndex; i <= n; i++) {

path.push_back(i);//处理节点

backtracking(n, k, i + 1);//递归

path.pop_back();//回溯

}

代码如下：

 1 class Solution {
 2 private:
 3         vector<vector<int>> result;
 4         vector<int> path;
 5         void backtracking (int n, int k, int startIndex) {
 6             if (path.size() == k) {
 7                 result.push_back(path);
 8                 return;
 9             }
10             for (int i = startIndex; i <= n; i++) {
11                 path.push_back(i);
12                 backtracking(n, k, i + 1);
13                 path.pop_back();
14             }
15         }
16 public:
17     vector<vector<int>> combine(int n, int k) {
18         result.clear();
19         path.clear();
20         backtracking(n, k , 1);
21         return result;
22     }
23 };