map按key和按value排序

看一个题：查找和排序题目：输入任意（用户，成绩）序列，可以获得成绩从高到低或从低到高的排列,相同成绩都按先录入排列在前的规则处理。例示： jack 70 peter 96 Tom 70 smith 67 从高到低成绩 peter 96 jack 70 Tom 70 smith 67 从低到高 smith 67 Tom 70 jack 70 peter 96

1、按照value排序 2、可以递增排序和递减排序 3、保证排序的稳定性

golang map按key排序

//golang的map不保证有序性，所以按key排序需要取出key，对key排序，再遍历输出value

package main



import (

    "fmt"

    "sort"

)



func main() {

    // To create a map as input

    m := make(map[int]string)

    m[1] = "a"

    m[2] = "c"

    m[0] = "b"



    // To store the keys in slice in sorted order

    var keys []int

    for k := range m {

        keys = append(keys, k)

    }

    sort.Ints(keys)



    // To perform the opertion you want

    for _, k := range keys {

        fmt.Println("Key:", k, "Value:", m[k])

    }

}

golang map按value排序

//要对golang map按照value进行排序，思路是直接不用map，用struct存放key和value，实现sort接口，就可以调用sort.Sort进行排序了。

// A data structure to hold a key/value pair.

type Pair struct {

    Key   string

    Value int

}



// A slice of Pairs that implements sort.Interface to sort by Value.

type PairList []Pair



func (p PairList) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }

func (p PairList) Len() int           { return len(p) }

func (p PairList) Less(i, j int) bool { return p[i].Value < p[j].Value }



// A function to turn a map into a PairList, then sort and return it.

func sortMapByValue(m map[string]int) PairList {

    p := make(PairList, len(m))

    i := 0

    for k, v := range m {

        p[i] = Pair{k, v}

    }

    sort.Sort(p)

    return p

}

golang map递增排序

//sort.Sort是递增排序，如果要实现递减排序，用sort.Reverse

package main



import (

    "fmt"

    "sort"

)



func main() {

    a := []int{4,3,2,1,5,9,8,7,6}

    sort.Sort(sort.Reverse(sort.IntSlice(a)))

    fmt.Println("After reversed: ", a)

}

golang map 排序的稳定性

//sort不保证排序的稳定性（两个相同的值，排序之后相对位置不变），排序的稳定性由sort.Stable来保证。

package main



import (

    "fmt"

    "sort"

)



type person struct {

  Name string

  Age int

}



type personSlice []person



func (s personSlice) Len() int { return len(s) }

func (s personSlice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

func (s personSlice) Less(i, j int) bool { return s[i].Age < s[j].Age }



func main() {

    a := personSlice {

      {

        Name: "AAA",

        Age: 55,

      },

      {

        Name: "BBB",

        Age: 22,

      },

      {

        Name: "CCC",

        Age: 0,

      },

      {

        Name: "DDD",

        Age: 22,

      },

      {

        Name: "EEE",

        Age: 11,

      },  

    }

    sort.Stable(a)

    fmt.Println(a)

}

C++按value排序、递增和递减、排序的稳定性

/看一下本题的C++解法，C++ sort的第三个参数用来定义排序方法，即按key还是value排序，递增还是递减排序等，stable_sort用来保证排序的稳定性，主要思路与golang解法相似，都是用struct封装key和value来代替map。

#include <iostream>

#include <vector>

#include <algorithm>

#include <string>

using namespace std;

struct student{

  string name;

    int score;

};

bool cmp0(const student &a, const student &b){

    // 从高到低排序

    return a.score > b.score;

}

bool cmp1(const student &a, const student &b){

    // 从低到高排序

    return a.score < b.score;

}

int main(){

    //freopen("in.txt", "r", stdin);

    //freopen("out.txt", "w", stdout);

    int N, type;

    while(cin >> N >> type){

        vector<student> stud(N);

 

        for(int i = 0; i < N; i ++){

            cin >> stud[i].name >> stud[i].score;

        }

        if(type == 0)

            stable_sort(stud.begin(), stud.end(), cmp0);   //稳定排序

        else

            stable_sort(stud.begin(), stud.end(), cmp1);

 

        for(int i = 0; i < N; i ++){

            cout << stud[i].name << " " << stud[i].score << endl;

        }

    }

 

    return 0;

}