565-ArrayNesting.go

package main

// 565. Array Nesting
// You are given an integer array nums of length n where nums is a permutation of the numbers in the range [0, n - 1].
// You should build a set s[k] = {nums[k], nums[nums[k]], nums[nums[nums[k]]], ... } subjected to the following rule:
//     The first element in s[k] starts with the selection of the element nums[k] of index = k.
//     The next element in s[k] should be nums[nums[k]], and then nums[nums[nums[k]]], and so on.
//     We stop adding right before a duplicate element occurs in s[k].

// Return the longest length of a set s[k].

// Example 1:
// Input: nums = [5,4,0,3,1,6,2]
// Output: 4
// Explanation: 
// nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.
// One of the longest sets s[k]:
// s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}

// Example 2:
// Input: nums = [0,1,2]
// Output: 1

// Constraints:
//     1 <= nums.length <= 10^5
//     0 <= nums[i] < nums.length
//     All the values of nums are unique.

import "fmt"

func arrayNesting(nums []int) int {
    res, visited := 0, make([]bool, len(nums))
    max := func (x, y int) int { if x > y { return x; }; return y; }
    for i := range nums {
        cur, count := i, 0
        for !visited[cur] {
            count++
            visited[cur] = true
            cur = nums[cur]
        }
        res = max(res, count)
    }
    return res
}

func main() {
    // Example 1:
    // Input: nums = [5,4,0,3,1,6,2]
    // Output: 4
    // Explanation: 
    // nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.
    // One of the longest sets s[k]:
    // s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}
    fmt.Println(arrayNesting([]int{5,4,0,3,1,6,2})) // 4
    // Example 2:
    // Input: nums = [0,1,2]
    // Output: 1
    fmt.Println(arrayNesting([]int{0,1,2})) // 1
}