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60 lines
1.0 KiB
Markdown
Executable File
60 lines
1.0 KiB
Markdown
Executable File
# [77. Combinations](https://leetcode.com/problems/combinations/)
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## 题目
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Given two integers *n* and *k*, return all possible combinations of *k* numbers out of 1 ... *n*.
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**Example**:
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Input: n = 4, k = 2
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Output:
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[
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[2,4],
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[3,4],
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[2,3],
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[1,2],
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[1,3],
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[1,4],
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]
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## 题目大意
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给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。
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## 解题思路
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- 计算排列组合中的组合，用 DFS 深搜即可，注意剪枝
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## 代码
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```
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package leetcode
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func combine(n int, k int) [][]int {
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if n <= 0 || k <= 0 || k > n {
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return [][]int{}
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}
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c, res := []int{}, [][]int{}
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generateCombinations(n, k, 1, c, &res)
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return res
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}
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func generateCombinations(n, k, start int, c []int, res *[][]int) {
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if len(c) == k {
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b := make([]int, len(c))
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copy(b, c)
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*res = append(*res, b)
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return
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}
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// i will at most be n - (k - c.size()) + 1
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for i := start; i <= n-(k-len(c))+1; i++ {
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c = append(c, i)
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generateCombinations(n, k, i+1, c, res)
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c = c[:len(c)-1]
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}
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return
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}
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``` |