[go language questions] go from 0 to entry 5: comprehensive review of map, conditional sentences and circular sentences

Preface

• This period is for learning Golang：Map Comprehensive review 、 Conditional statements 、 Loop exercises , If you don't understand something, you can comment and discuss it ！
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Q1：Map- String formation

Problem description ： Given two strings des and src , Judge des Can it be done by src The characters inside make up ,// If possible , return true ; Otherwise return to false,src Each character in can only be in des Used once in .

Related knowledge ：
1、for range Traversal string .
2、cnt[ch-‘a’] Implicit conversion byte To int type .
3、 The index of the array can act as a map Of key, To show the only .

Sample input ：“ab”,“aab”
Sample output ：true

Case code ：
Ideas ： Let's play one. map Used to save which elements can be used With a -1 that will do . If there is no direct return failure .

//import "fmt"
/** *  The class name in the code 、 Method name 、 The parameter name has been specified , Do not modify , Return the value specified by the method directly  * * * @param des string character string  * @param src string character string  * @return bool Boolean type  */
func canConstruct(des string, src string) bool {
    
	// write code here
	have := make(map[byte]int)
	s := []byte(src)
	for _, i := range s {
    
		have[i]++
	}

	p := []byte(des)
	for _, i := range p {
    
		if have[i] == 0 {
    
			return false
		}
		have[i]--
	}
	return true
}

Q2：Map- Numbers that don't repeat

Problem description ： Given an array , Find all the non repeating numbers in the array , And output in the order from small to large .

Related knowledge ：
1、map use make Method to initialize
2、 Slicing can be done with []int{} To initialize
3、for range Traversing slices
4、_,ok :=map[key] How to judge m Medium key Whether there is
5、 For slicing append Method

Sample input ：[1,1,2,2,3,3,4,4,5,5]
Sample output ：[]

Sample input ：[3,3,2,2,5,5,1,2,2]
Sample output ：[1]

Case code ：

import "sort"
/** *  The class name in the code 、 Method name 、 The parameter name has been specified , Do not modify , Return the value specified by the method directly  *  Finally, there should be one   The process of sorting   Use sort The sorting provided is sufficient  * @param s int Integer one-dimensional array  * @return int Integer one-dimensional array  */
func getNoRepeat(s []int) []int {
    
	// write code here
	var ans []int
	have := make(map[int]int)
	for _, i := range s {
    
		if _, ok := have[i]; ok == false {
    
			have[i] = 1
		}else{
    
			have[i]++
		}
	}
	for i, j := range have{
    
		if j == 1{
    
			ans = append(ans, i)
		}
	}
    sort.Ints(ans) 
	return ans
}

Q3： Conditional statements - Age determination

Problem description ： The known age segments are as follows , baby ( born 0-1 year )、 Young children (1-4 year ) contain 1 year 、 children (5-11) contain 5 year 、 juvenile (12-18) contain 12 year 、 youth (19-35) contain 19 year 、 middle-aged (36-59) contain 36 year 、 The elderly (60 above ) contain 60 year , Enter a person's age , Return to the appropriate age group .

Related knowledge ：
1、if Any number of... Can be followed else if sentence .condition The evaluation of is carried out from top to bottom , Until some if perhaps else if Medium condition by true when , Execute the corresponding code block . If there is no one conditon by true, execute else Code block in .

Sample input ：35
Sample output ：“ youth ”

Case code ：

//import "fmt"
/** *  The class name in the code 、 Method name 、 The parameter name has been specified , Do not modify , Return the value specified by the method directly  * @param age int integer   Age  * @return string character string  */
func getAge( age int ) string {
    
	// write code here
	var ans string
	switch {
    
	case age <1 && age >= 0:
		ans = " baby "
	case age >=1 && age <= 4:
		ans = " Young children "
	case age >= 5 && age <= 11:
		ans = " children "
	case age >= 12 && age <= 18:
		ans = " juvenile "
	case age >= 19 && age <= 35:
		ans = " youth "
	case age >=36 && age <=59:
		ans = " middle-aged "
	case age >= 60:
		ans = " The elderly "
	}
	return  ans
}

Q4： Conditional statements - Grade judgment

Problem description ： Output the grade according to the score , The decision rules are as follows The score is below 60 Not pass ,60-80 contain 60 It's medium , 80-90 contain 80 For good ,90 Points above include 90 For excellence .

Related knowledge ：
1、switch Statements are used to perform different actions based on different conditions , every last case Branches are all unique , Test from top to bottom , Until it matches . Golang switch Branch expressions can be of any type , Not limited to constants . Omission break, Automatically terminate by default .
switch var1 {
case val1:
…
case val2:
…
default:
…
}

Sample input ：59
Sample output ：“ fail, ”

Case code ：

func judgeScore(score int) string {
    
    // write code here
    var grade string
    switch {
    
    case score < 60:
        grade = " fail, "
    case score >= 60 && score < 80:
        grade = " secondary "
    case score >= 80 && score < 90:
        grade = " good "
    case score >= 90:
        grade = " good "
    }
    return grade
}

Q5： Loop statement - Multiplication table

Problem description ： Print 9*9 Multiplication table .

Related knowledge ：
1、golang in for One or more... Are nested in the loop for loop , The code format is as follows ：
for [condition | ( init; condition; increment ) | Range]
{
for [condition | ( init; condition; increment ) | Range]
{
statement(s)
}
statement(s)
}
init： It's usually an assignment expression , Assign initial values to control variables ;
condition： A relational or logical expression , Cycle control conditions ;
increment： It's usually an assignment expression , Increment or decrement of a control variable .
statement： Loop statement
2、goalng in ,fmt.printf Format printing %d Representation number ,-3d Indicates left alignment , Occupy 3 position \n Represents the next line .

Sample input ：
Sample output ：

1*1=1
1*2=2  2*2=4
1*3=3  2*3=6  3*3=9
1*4=4  2*4=8  3*4=12 4*4=16
1*5=5  2*5=10 3*5=15 4*5=20 5*5=25
1*6=6  2*6=12 3*6=18 4*6=24 5*6=30 6*6=36
1*7=7  2*7=14 3*7=21 4*7=28 5*7=35 6*7=42 7*7=49
1*8=8  2*8=16 3*8=24 4*8=32 5*8=40 6*8=48 7*8=56 8*8=64
1*9=9  2*9=18 3*9=27 4*9=36 5*9=45 6*9=54 7*9=63 8*9=72 9*9=81

Case code ：

import "fmt"
func main() {
    
	fmt.Println("1*1=1")
	for i := 2; i <= 9; i++ {
    
		for j := 1; j <= i-1; j++ {
    
			str := fmt.Sprintf("%d*%d=%-3d", j, i,j*i)
            
			fmt.Printf("%s", str)
		}
		str := fmt.Sprintf("%d*%d=%d", i, i, i*i)
		fmt.Printf("%s\n", str)
	}
}

Q6： Loop statement - Coordinate transformation

Problem description ： Known one mn Two dimensional array , Index of elements in a two-dimensional array （x,y） It can be expressed as a two-dimensional coordinate , Now convert this two-dimensional coordinate to one-dimensional coordinate , One dimensional coordinates =xn+y. Return this one-dimensional array .

Related knowledge ：
1、 Arrays can be accessed by subscripts , The subscript is from 0 Start , The last element subscript is ：len-1
for i := 0; i < len(a); i++ {
}
for index, v := range a {
}
2、 Length is part of the array type , therefore ,var a[5] int and var a[10]int It's a different type .
3、 To define an array ：var a [len]int, such as ：var a [5]int, Array length must be constant , And it's part of the type . Once defined , The length cannot change .

Sample input ：[[1,2,3],[4,5,6],[7,8,9]]
Sample output ：[1,2,3,4,5,6,7,8,9]

Case code ：

//import "fmt"
/** *  The class name in the code 、 Method name 、 The parameter name has been specified , Do not modify , Return the value specified by the method directly  * @param array int Two dimensional arrays of integers  * @return int Integer one-dimensional array  */
func transform(array [][]int) []int {
    
	// write code here
	m := len(array)
	n := len(array[0])
	var arr []int = make([]int, m*n)
	i := 0
	for a := 0; a < m; a++ {
    
		for b := 0; b < n; b++ {
    
			arr[i] = array[a][b]
			i++
		}
	}
	return arr
}

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