163. 缺失的区间 Missing Ranges

给定一个排序的整数数组 nums ，其中元素的范围在闭区间 [lower, upper] 当中，返回不包含在数组中的缺失区间。

示例：

输入: nums = [0, 1, 3, 50, 75], lower = 0, upper = 99
输出: [“2”, “4->49”, “51->74”, “76->99”]

代码1：

package main

import (
	"fmt"
	"strconv"
)

func findMissingRanges(nums []int, lower int, upper int) []string {
	res := make([]string, 0)
	start := lower - 1
	for i := 0; i <= len(nums); i++ {
		end := upper + 1
		if i < len(nums) {
			end = nums[i]
		}
		if end-start == 2 {
			res = append(res, strconv.Itoa(start+1))
		} else if end-start > 2 {
			res = append(res, strconv.Itoa(start+1)+"->"+strconv.Itoa(end-1))
		}
		start = end
	}
	return res
}

func main() {
	nums := []int{0, 1, 3, 50, 75}
	lower := 0
	upper := 99
	fmt.Println(findMissingRanges(nums, lower, upper))
}

代码2：

package main

import (
	"fmt"
	"strconv"
)

func findMissingRanges(nums []int, lower int, upper int) []string {
	res := make([]string, 0)
	start := lower
	for i := 0; i < len(nums); i++ {
		if nums[i] < start {
			continue
		}
		if nums[i] == start {
			start++
			continue
		}
		end := nums[i] - 1
		if start == end {
			res = append(res, strconv.Itoa(start))
		} else {
			res = append(res, strconv.Itoa(start)+"->"+strconv.Itoa(end))
		}
		start = nums[i] + 1
	}
	if start <= upper {
		if start == upper {
			res = append(res, strconv.Itoa(start))
		} else {
			res = append(res, strconv.Itoa(start)+"->"+strconv.Itoa(upper))
		}
	}
	return res
}

func main() {
	nums := []int{0, 1, 3, 50, 75}
	lower := 0
	upper := 99
	fmt.Println(findMissingRanges(nums, lower, upper))
}

输出：

[2 4->49 51->74 76->99]

164. 最大间距 Maximum Gap

给定一个无序的数组 nums，返回 数组在排序之后，相邻元素之间最大的差值 。如果数组元素个数小于 2，则返回 0 。

您必须编写一个在「线性时间」内运行并使用「线性额外空间」的算法。

示例 1:

输入: nums = [3,6,9,1]
输出: 3
解释: 排序后的数组是 [1,3,6,9], 其中相邻元素 (3,6) 和 (6,9) 之间都存在最大差值 3。

示例 2:

输入: nums = [10]
输出: 0
解释: 数组元素个数小于 2，因此返回 0。

提示:

1 <= nums.length <= 10^5
0 <= nums[i] <= 10^9

代码1：基数排序

package main

import "fmt"

func maximumGap(nums []int) int {
	n := len(nums)
	if n < 2 {
		return 0
	}
	maxNum := nums[0]
	for _, num := range nums {
		if num > maxNum {
			maxNum = num
		}
	}
	exp := 1
	buf := make([]int, n)
	for maxNum/exp > 0 {
		count := make([]int, 10)
		for _, num := range nums {
			digit := (num / exp) % 10
			count[digit]++
		}
		for i := 1; i < 10; i++ {
			count[i] += count[i-1]
		}
		for i := n - 1; i >= 0; i-- {
			digit := (nums[i] / exp) % 10
			count[digit]--
			buf[count[digit]] = nums[i]
		}
		copy(nums, buf)
		exp *= 10
	}
	maxGap := 0
	for i := 1; i < n; i++ {
		gap := nums[i] - nums[i-1]
		if gap > maxGap {
			maxGap = gap
		}
	}
	return maxGap
}

func main() {
	nums := []int{3, 6, 9, 1}
	fmt.Println(maximumGap(nums))
	nums = []int{10}
	fmt.Println(maximumGap(nums))
}

代码2：桶排序

package main

import "fmt"

func maximumGap(nums []int) int {
	n := len(nums)
	if n < 2 {
		return 0
	}
	minNum, maxNum := nums[0], nums[0]
	for _, num := range nums {
		if num < minNum {
			minNum = num
		} else if num > maxNum {
			maxNum = num
		}
	}
	if minNum == maxNum {
		return 0
	}
	bucketSize := max(1, (maxNum-minNum)/(n-1))
	bucketNum := (maxNum-minNum)/bucketSize + 1
	buckets := make([][]int, bucketNum)
	for _, num := range nums {
		bucketIndex := (num - minNum) / bucketSize
		if buckets[bucketIndex] == nil {
			buckets[bucketIndex] = []int{num, num}
		} else {
			if num < buckets[bucketIndex][0] {
				buckets[bucketIndex][0] = num
			} else if num > buckets[bucketIndex][1] {
				buckets[bucketIndex][1] = num
			}
		}
	}
	maxGap := 0
	prevMax := minNum
	for _, bucket := range buckets {
		if bucket != nil {
			maxGap = max(maxGap, bucket[0]-prevMax)
			prevMax = bucket[1]
		}
	}
	return maxGap
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func main() {
	nums := []int{3, 6, 9, 1}
	fmt.Println(maximumGap(nums))
	nums = []int{10}
	fmt.Println(maximumGap(nums))
}

输出：

3
0