1700-NumberOfStudentsUnableToEatLunch.go

package main

// 1700. Number of Students Unable to Eat Lunch
// The school cafeteria offers circular and square sandwiches at lunch break, referred to by numbers 0 and 1 respectively. 
// All students stand in a queue. Each student either prefers square or circular sandwiches.

// The number of sandwiches in the cafeteria is equal to the number of students. 
// The sandwiches are placed in a stack. At each step:
//     If the student at the front of the queue prefers the sandwich on the top of the stack, they will take it and leave the queue.
//     Otherwise, they will leave it and go to the queue's end.

// This continues until none of the queue students want to take the top sandwich and are thus unable to eat.

// You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) 
// and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). 
// Return the number of students that are unable to eat.

// Example 1:
// Input: students = [1,1,0,0], sandwiches = [0,1,0,1]
// Output: 0 
// Explanation:
// - Front student leaves the top sandwich and returns to the end of the line making students = [1,0,0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [0,0,1,1].
// - Front student takes the top sandwich and leaves the line making students = [0,1,1] and sandwiches = [1,0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [1,1,0].
// - Front student takes the top sandwich and leaves the line making students = [1,0] and sandwiches = [0,1].
// - Front student leaves the top sandwich and returns to the end of the line making students = [0,1].
// - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1].
// - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = [].
// Hence all students are able to eat.

// Example 2:
// Input: students = [1,1,1,0,0,1], sandwiches = [1,0,0,0,1,1]
// Output: 3

// Constraints:
//     1 <= students.length, sandwiches.length <= 100
//     students.length == sandwiches.length
//     sandwiches[i] is 0 or 1.
//     students[i] is 0 or 1.

import "fmt"

func countStudents(students []int, sandwiches []int) int {
    // 统计出喜欢  circular 0 and square 1 sandwiches 的学生数量
    hash := make(map[int]int, 2)
    for _, v := range students {
        hash[v]++
    }
    // 发放 sandwiches
    for _, v := range sandwiches {
        // sandwiches 发放顺序不能变,喜欢该类型的三明治的学生没有了
        // 返回喜欢其它类型 v^1 的学生数量即可
        if hash[v] == 0 {
            // fmt.Printf("v = %v, v^1 = %v \n",v, v^1)
            return hash[v^1]
        }
        hash[v]--
    }
    return 0
}

// 用数组来替代 map
func countStudents1(students []int, sandwiches []int) int {
    // 统计出喜欢  circular 0 and square 1 sandwiches 的学生数量
    arr := []int{0,0}
    for _, v := range students {
        arr[v]++
    }
    // 发放 sandwiches
    for _, v := range sandwiches {
        // sandwiches 发放顺序不能变,喜欢该类型的三明治的学生没有了
        // 返回喜欢其它类型 v^1 的学生数量即可
        if arr[v] == 0 {
            // fmt.Printf("v = %v, v^1 = %v \n",v, v^1)
            return arr[v^1]
        }
        arr[v]--
    }
    return 0
}

func main() {
    // - Front student leaves the top sandwich and returns to the end of the line making students = [1,0,0,1].
    // - Front student leaves the top sandwich and returns to the end of the line making students = [0,0,1,1].
    // - Front student takes the top sandwich and leaves the line making students = [0,1,1] and sandwiches = [1,0,1].
    // - Front student leaves the top sandwich and returns to the end of the line making students = [1,1,0].
    // - Front student takes the top sandwich and leaves the line making students = [1,0] and sandwiches = [0,1].
    // - Front student leaves the top sandwich and returns to the end of the line making students = [0,1].
    // - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1].
    // - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = [].
    // Hence all students are able to eat.
    fmt.Println(countStudents([]int{1,1,0,0},[]int{0,1,0,1})) // 0
    // students=[1,1,1,0,0,1]   sandwiches=[1,0,0,0,1,1]
    // students=[1,1,0,0,1]     sandwiches=[0,0,0,1,1]
    // students=[1,0,0,1,1]     sandwiches=[0,0,0,1,1]
    // students=[0,0,1,1,1]     sandwiches=[0,0,0,1,1]
    // students=[0,1,1,1]       sandwiches=[0,0,1,1]
    // students=[1,1,1]         sandwiches=[0,1,1]
    // res = len(students)
    fmt.Println(countStudents([]int{1,1,1,0,0,1},[]int{1,0,0,0,1,1})) // 3

    fmt.Println(countStudents1([]int{1,1,0,0},[]int{0,1,0,1})) // 0
    fmt.Println(countStudents1([]int{1,1,1,0,0,1},[]int{1,0,0,0,1,1})) // 3
}