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96 lines
1.7 KiB
Markdown
Executable File
96 lines
1.7 KiB
Markdown
Executable File
# [60. Permutation Sequence](https://leetcode.com/problems/permutation-sequence/)
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## 题目
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The set `[1,2,3,...,*n*]` contains a total of *n*! unique permutations.
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By listing and labeling all of the permutations in order, we get the following sequence for *n* = 3:
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1. `"123"`
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2. `"132"`
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3. `"213"`
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4. `"231"`
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5. `"312"`
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6. `"321"`
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Given *n* and *k*, return the *k*th permutation sequence.
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**Note**:
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- Given *n* will be between 1 and 9 inclusive.
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- Given *k* will be between 1 and *n*! inclusive.
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**Example 1**:
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```
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Input: n = 3, k = 3
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Output: "213"
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```
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**Example 2**:
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```
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Input: n = 4, k = 9
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Output: "2314"
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```
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## 题目大意
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给出集合 [1,2,3,…,n]，其所有元素共有 n! 种排列。
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按大小顺序列出所有排列情况，并一一标记，当 n = 3 时, 所有排列如下："123"，"132"，"213"，"231"，"312"，"321"，给定 n 和 k，返回第 k 个排列。
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## 解题思路
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- 用 DFS 暴力枚举，这种做法时间复杂度特别高，想想更优的解法。
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## 代码
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```go
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package leetcode
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import (
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"fmt"
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"strconv"
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)
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func getPermutation(n int, k int) string {
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if k == 0 {
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return ""
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}
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used, p, res := make([]bool, n), []int{}, ""
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findPermutation(n, 0, &k, p, &res, &used)
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return res
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}
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func findPermutation(n, index int, k *int, p []int, res *string, used *[]bool) {
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fmt.Printf("n = %v index = %v k = %v p = %v res = %v user = %v\n", n, index, *k, p, *res, *used)
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if index == n {
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*k--
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if *k == 0 {
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for _, v := range p {
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*res += strconv.Itoa(v + 1)
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}
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}
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return
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}
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for i := 0; i < n; i++ {
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if !(*used)[i] {
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(*used)[i] = true
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p = append(p, i)
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findPermutation(n, index+1, k, p, res, used)
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p = p[:len(p)-1]
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(*used)[i] = false
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}
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}
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return
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}
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``` |