Project Euler with Golang

# Go言語はじめてみた

## 経緯

1. golangでゲームを作ったら快適に開発できそう！
1. リファレンスを読んでいくと事はそんなに簡単じゃないっぽい。
1. golangを選択すべきか、選択すべきでないか、それが問題だ。
1. どちらも決め手に欠けるので、実際に書いてみて判断するか。
1. 「Project Euler」ってヤツが面白そうだから、これをお題にしよう！

## Project Euler

https://projecteuler.net/

http://odz.sakura.ne.jp/projecteuler/index.php?Project%20Euler

## Problem 1 - 10

https://qiita.com/wing-tail/items/9e6b10abff6ee1502ce7

## Problem 11

```Go:Main.go
package main
import (
    "fmt"
    "bufio"
    "os"
    "strings"
    "strconv"
)
func main(){
    size := 20
    input_matrix := make([][]int, size)
    count := 0
    stdin := bufio.NewScanner(os.Stdin)
    for stdin.Scan() {
        text := stdin.Text()
        input_slice := strings.Split(text, " ")
        slice := make([]int, size)
        for key, str := range input_slice {
            val, _ := strconv.Atoi(str)
            slice[key] = val
        }
        input_matrix[count] = slice
        count++
    }
    ret := 0
    for i := 0; i < size; i++ {
        for j := 0; j < size; j++ {
            if j > size - 4 && i > size - 4 {
                continue
            }
            if j < size - 3 && i < size - 3 {
                check_diagonal_down := input_matrix[i][j] * input_matrix[i + 1][j + 1] * input_matrix[i + 2][j + 2] * input_matrix[i + 3][j + 3]
                if ret < check_diagonal_down {
                    ret = check_diagonal_down
                }
            }
            if j < size - 3 && i > 2 {
                check_diagonal_up := input_matrix[i][j] * input_matrix[i - 1][j + 1] * input_matrix[i - 2][j + 2] * input_matrix[i - 3][j + 3]
                if ret < check_diagonal_up {
                    ret = check_diagonal_up
                }
            }
            if j < size - 3 {
                check_horizontal := input_matrix[i][j] * input_matrix[i][j + 1] * input_matrix[i][j + 2] * input_matrix[i][j + 3]
                if ret < check_horizontal {
                    ret = check_horizontal
                }
            }
            if i < size - 3 {
                check_vertical := input_matrix[i][j] * input_matrix[i + 1][j] * input_matrix[i + 2][j] * input_matrix[i + 3][j]
                if ret < check_vertical {
                    ret = check_vertical
                }
            }
        }
    }
    fmt.Println(ret)
}
```

```Go:input
08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
```

## Problem 12

```Go:Main.go
package main
import (
    "fmt"
)
func main(){
    tri_sum := 1
    count := 1
    for {
        count++
        tri_sum += count
        check_divide := tri_sum
        check_num := 2
        divisors := 1
        for {
            divide_count := 1
            for {
                if check_divide % check_num != 0 {
                    divisors *= divide_count
                    break
                }
                check_divide = int(check_divide / check_num)
                divide_count++
            }
            if check_divide == 1 {
                break
            }
            check_num++
        }
        if divisors > 500 {
            break
        }
    }
    fmt.Println(tri_sum)
}
```

## Problem 13

```Go:Main.go
package main
import (
    "fmt"
    "bufio"
    "os"
    "math/big"
    "strconv"
)
func main(){
    sum := big.NewInt(0)
    stdin := bufio.NewScanner(os.Stdin)
    for stdin.Scan() {
        input := stdin.Text()
        val, _ := new(big.Int).SetString(input, 10)
        sum = new(big.Int).Add(sum, val)
    }
    sum_string := sum.String()
    sum_rune := []rune(sum_string)
    var ret_string string
    for i := 0; i < 10; i++ {
        ret_string += string(sum_rune[i])
    }
    ret, _ := strconv.Atoi(ret_string)
    fmt.Println(ret)
}
```

```Go:input
37107287533902102798797998220837590246510135740250
46376937677490009712648124896970078050417018260538
74324986199524741059474233309513058123726617309629
91942213363574161572522430563301811072406154908250
23067588207539346171171980310421047513778063246676
89261670696623633820136378418383684178734361726757
28112879812849979408065481931592621691275889832738
44274228917432520321923589422876796487670272189318
47451445736001306439091167216856844588711603153276
70386486105843025439939619828917593665686757934951
62176457141856560629502157223196586755079324193331
64906352462741904929101432445813822663347944758178
92575867718337217661963751590579239728245598838407
58203565325359399008402633568948830189458628227828
80181199384826282014278194139940567587151170094390
35398664372827112653829987240784473053190104293586
86515506006295864861532075273371959191420517255829
71693888707715466499115593487603532921714970056938
54370070576826684624621495650076471787294438377604
53282654108756828443191190634694037855217779295145
36123272525000296071075082563815656710885258350721
45876576172410976447339110607218265236877223636045
17423706905851860660448207621209813287860733969412
81142660418086830619328460811191061556940512689692
51934325451728388641918047049293215058642563049483
62467221648435076201727918039944693004732956340691
15732444386908125794514089057706229429197107928209
55037687525678773091862540744969844508330393682126
18336384825330154686196124348767681297534375946515
80386287592878490201521685554828717201219257766954
78182833757993103614740356856449095527097864797581
16726320100436897842553539920931837441497806860984
48403098129077791799088218795327364475675590848030
87086987551392711854517078544161852424320693150332
59959406895756536782107074926966537676326235447210
69793950679652694742597709739166693763042633987085
41052684708299085211399427365734116182760315001271
65378607361501080857009149939512557028198746004375
35829035317434717326932123578154982629742552737307
94953759765105305946966067683156574377167401875275
88902802571733229619176668713819931811048770190271
25267680276078003013678680992525463401061632866526
36270218540497705585629946580636237993140746255962
24074486908231174977792365466257246923322810917141
91430288197103288597806669760892938638285025333403
34413065578016127815921815005561868836468420090470
23053081172816430487623791969842487255036638784583
11487696932154902810424020138335124462181441773470
63783299490636259666498587618221225225512486764533
67720186971698544312419572409913959008952310058822
95548255300263520781532296796249481641953868218774
76085327132285723110424803456124867697064507995236
37774242535411291684276865538926205024910326572967
23701913275725675285653248258265463092207058596522
29798860272258331913126375147341994889534765745501
18495701454879288984856827726077713721403798879715
38298203783031473527721580348144513491373226651381
34829543829199918180278916522431027392251122869539
40957953066405232632538044100059654939159879593635
29746152185502371307642255121183693803580388584903
41698116222072977186158236678424689157993532961922
62467957194401269043877107275048102390895523597457
23189706772547915061505504953922979530901129967519
86188088225875314529584099251203829009407770775672
11306739708304724483816533873502340845647058077308
82959174767140363198008187129011875491310547126581
97623331044818386269515456334926366572897563400500
42846280183517070527831839425882145521227251250327
55121603546981200581762165212827652751691296897789
32238195734329339946437501907836945765883352399886
75506164965184775180738168837861091527357929701337
62177842752192623401942399639168044983993173312731
32924185707147349566916674687634660915035914677504
99518671430235219628894890102423325116913619626622
73267460800591547471830798392868535206946944540724
76841822524674417161514036427982273348055556214818
97142617910342598647204516893989422179826088076852
87783646182799346313767754307809363333018982642090
10848802521674670883215120185883543223812876952786
71329612474782464538636993009049310363619763878039
62184073572399794223406235393808339651327408011116
66627891981488087797941876876144230030984490851411
60661826293682836764744779239180335110989069790714
85786944089552990653640447425576083659976645795096
66024396409905389607120198219976047599490197230297
64913982680032973156037120041377903785566085089252
16730939319872750275468906903707539413042652315011
94809377245048795150954100921645863754710598436791
78639167021187492431995700641917969777599028300699
15368713711936614952811305876380278410754449733078
40789923115535562561142322423255033685442488917353
44889911501440648020369068063960672322193204149535
41503128880339536053299340368006977710650566631954
81234880673210146739058568557934581403627822703280
82616570773948327592232845941706525094512325230608
22918802058777319719839450180888072429661980811197
77158542502016545090413245809786882778948721859617
72107838435069186155435662884062257473692284509516
20849603980134001723930671666823555245252804609722
53503534226472524250874054075591789781264330331690
```

## Problem 14

```Go:Main.go
package main
import (
    "fmt"
    "math"
)
func main(){
    max_start := 1
    max_count := 1
    limit := int(math.Pow10(6))
    for i := 1; i < limit; i++ {
        check_num := i
        count := 1
        for {
            if check_num == 1 {
                if max_count < count {
                    max_count = count
                    max_start = i
                }
                break
            }
            if check_num % 2 != 0 {
                check_num = 3 * check_num + 1
                count++
                continue
            }
            check_num = int(check_num / 2)
            count++
            continue
        }
    }
    fmt.Println(max_start)
}
```

## Problem 15

```Go:Main.go
package main
import (
    "fmt"
    "math"
)
func main(){
    input_column := 20
    input_line := 20
    input_range := make([]bool, input_line)
    sum := input_column + input_line
    ret := 1
    for i := sum; i > input_column; i-- {
        ret *= i
        for key, value := range input_range {
            if value == true {
                continue
            }
            check_num := key + 1
            if ret % check_num != 0 {
                continue
            }
            ret = int(ret / check_num)
            input_range[key] = true
            if ret == 1 {
                break
            }
        }
    }
    fmt.Println(ret)
}
```

## Problem 16

```Go:Main.go
package main
import (
    "fmt"
)
func main(){
    input := 1000
    digits := []int{1}
    for i := 1; i < input + 1; i++ {
        max_digit := len(digits)
        increase_digit := 0
        for j := 0; j < max_digit; j++ {
            value := digits[j] * 2 + increase_digit
            if value < 10 {
                digits[j] = value
                increase_digit = 0
                continue
            }
            digits[j] = value - 10
            if j + 1 == max_digit {
                digits = append(digits, 1)
                break
            }
            increase_digit = 1
        }
    }
    ret := 0;
    for _, value := range digits {
        ret += value
    }
    fmt.Println(ret)
}
```

## Problem 17

```Go:Main.go
package main
import (
    "fmt"
)
func main(){
    strcount_range_under_ten := []int{3, 3, 5, 4, 4, 3, 5, 5, 4}
    strcount_range_under_twenty := []int{3, 6, 6, 8, 8, 7, 7, 9, 8, 8}
    strcount_range_for_deca := []int{6, 5, 6, 5, 5, 7, 6, 6}
    strcount_handret := 7
    strcount_and := 3
    strcount_thousand := 11
    input := 1000
    ret := 0
    for i := 0; i < input + 1; i++ {
        check_num := i
        if check_num > 999 {
            ret += strcount_thousand
            break
        }
        if check_num > 99 {
            handred_key := int(check_num / 100) - 1
            ret += strcount_range_under_ten[handred_key]
            ret += strcount_handret
            check_num = check_num % 100
            if check_num > 0 {
                ret += strcount_and
            }
        }
        if check_num > 19 {
            deca_key := int((check_num - 20) / 10)
            ret += strcount_range_for_deca[deca_key]
            check_num = (check_num - 20) % 10
        }
        if check_num > 9 {
            key := check_num - 10
            ret += strcount_range_under_twenty[key]
            continue
        }
        if check_num == 0 {
            continue
        }
        ret += strcount_range_under_ten[check_num - 1]
    }
    fmt.Println(ret)
}
```