Analysis of the Lottery

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General Lottery question

Problem description

User random draw, data as follows:

// map中，key代表用户名，value代表成用户下单数var users map[string]int64 = map[string]int64{  "a": 10,  "b": 6,  "c": 3,  "d": 12,  "f": 1,}

Ideas

Random problem, usually is a random function from a certain range of random extraction of a value, then the value corresponding to the winning user

Here, if we can set a corresponding index for each element in the map, that is, to convert to an array , is it possible to solve the problem?

Code implementation

func GetAwardUserName(users map[string]int64) (name string) {    size := len(users)    awardIndex := rand.Intn(size)    i := 0    for userName, _ := range users {        if i == awardIndex {            name = userName            return        }        i++    }    return}

Unit Test

func Test_GetAwardUserName(t *testing.T) {    var users map[string]int64 = map[string]int64{        "a": 10,        "b": 6,        "c": 3,        "d": 12,        "f": 1,    }    rand.Seed(time.Now().Unix())    awardCount := make(map[string]int)    for i := 0; i <= 1000000; i++ {        awardName := GetAwardUserName(users)        if count, ok := awardCount[awardName]; ok {            awardCount[awardName] = count + 1        } else {            awardCount[awardName] = 0        }    }    for n, c := range awardCount {        fmt.Printf("%v:%v\n",n,c)    }}

Test results:

In order to verify the correctness of the winning probability, the loop executes 1 million times, each user wins the number basically is about 200,000, each user's winning probability is equal

c:200102f:199853b:198942a:200395d:200704

Weight Draw

Problem Description:

The data structure is consistent with the lottery, but here the probability of winning is proportional to the number of users ' orders.

Ideas

= = or random function to obtain a numerical value, the value corresponding to the user is the award-winning user ; here to achieve the number of orders to the winning probability of the problem, that is, = = order number corresponding to a certain range of random numbers, the larger the number of orders, the larger the range, random chatter in the range of the probability of the greater =

Code implementation

func getAwardUser_weight(users map[string]int64) (name string) {    type awardUser struct {        name   string        offset int64        count  int64    }    userSli := make([]*awardUser, 0,len(users))    var sumCount int64 = 0    for n, c := range users {        a := awardUser{            name:   n,            offset: sumCount,            count:  c,        }        //整理所有用户的count数据为数轴        userSli = append(userSli, &a)        sumCount += c    }    awardIndex := rand.Int63n(sumCount)    for _, u := range userSli {        //判断获奖index落在那个用户区间内        if u.offset+u.count>awardIndex {            name = u.name            return        }    }    return}

Unit Test

func Test_getAwardUser_weight(t *testing.T) {    var users map[string]int64 = map[string]int64{        "a": 10,        "b": 6,        "c": 3,        "d": 12,        "f": 1,    }    rand.Seed(time.Now().Unix())    awardCount := make(map[string]int)    for i := 0; i <= 100000; i++ {        awardName := getAwardUser_weight(users)        if count, ok := awardCount[awardName]; ok {            awardCount[awardName] = count + 1        } else {            awardCount[awardName] = 0        }    }    for n,c := range awardCount {        fmt.Printf("%v:%v \n",n,c)    }}

Test results:

Loop traversed 1 million times, the number of awards, in proportion to the number of orders of the user

Summarize

solve practical problems, often have a mathematical model to correspond to, such as lottery problems, can be converted to junior high school axis knowledge, draw a sketch, easy to understand, do not need more advanced mathematical knowledge

The problem itself is not difficult, it is important to switch ideas, to simplify the abstract problem into a specific mathematical problems, and then to solve