刷题笔记day27-回溯算法1

理论基础

77. 组合

class Solution:
    path: list = list()
    result: List[List[int]] = list()
    def traversal(self, left: int, n: int, k: int):
        # 终止条件
        if (len(self.path) == k):
            # 这里面需要用浅拷贝，而不能是引用
            self.result.append(copy.copy(self.path))
            # print(self.path)
            return 
        
        # 2、迭代所有
        for i in range(left, n+1):
            self.path.append(i)
            self.traversal(i+1, n, k)
            del self.path[-1]
        
        return 


    def combine(self, n: int, k: int) -> List[List[int]]:
        # 先清空，避免多轮测试
        self.path.clear()
        self.result.clear()
        self.traversal(1, n, k)
        return self.result

go的代码

// 算法思路：终止条件+广度遍历+回溯，撤销删除
import "fmt"

var result [][]int
var path []int

func combine(n int, k int) [][]int {
    result = [][]int{}
    path = []int{}
    nfs(n, k, 1)
    return result
}


func nfs(n, k, startIndex int) bool {
    // 终止条件
    if (len(path) == k) {
        var tmp  = make([]int, len(path))
        copy(tmp, path)
        result = append(result, tmp)
        return true
    }
    // 
    for i := startIndex; i <= n; i++ {
        // 处理节点
        path = append(path, i)
        nfs(n, k, i+1)
        // 回溯
        if len(path) > 0 {
            path = path[:len(path)-1]
        }
    }
    return true
}