回答編集履歴
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別解を追加
answer
CHANGED
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@@ -5,7 +5,7 @@
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5
5
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import java.util.Scanner;
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6
6
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7
7
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class Main {
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8
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-
public static void main
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8
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public static void main(String[] args) {
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9
9
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Scanner sc = new Scanner(System.in);
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10
10
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System.out.println("4桁の数字を入力してください");
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11
11
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String number = sc.next();
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@@ -51,4 +51,76 @@
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51
51
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```
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52
52
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53
53
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演算は左から順に実行。
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54
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-
割り算は整数の除算(小数点以下切り捨て)。
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54
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割り算は整数の除算(小数点以下切り捨て)。
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55
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56
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**追記**
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57
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ビット演算を使うと、 forの三重ループがひとつの for文になります。
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58
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```Java
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59
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for (int i = 0; i < 1<<6; i++) {
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60
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int[] op = { i>>4 & 3, i >>2 & 3, i & 3 };
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61
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if (calc(num, op) == result) print(num, op, result);
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62
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}
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```
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64
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あるいは、 forの三重ループのところで計算をすると、計算回数が減らせます。
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65
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```Java
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66
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for (op[0] = 0; op[0] < 4; op[0]++) {
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67
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int a = calc(num[0], op[0], num[1]);
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for (op[1] = 0; op[1] < 4; op[1]++) {
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int b = calc(a, op[1], num[2]);
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70
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for (op[2] = 0; op[2] < 4; op[2]++)
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71
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if (calc(b, op[2], num[3]) == result)
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print(num, op, result);
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}
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}
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76
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private static int calc(int a, int op, int b) {
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switch (op) {
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78
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case 0: return a + b;
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case 1: return a - b;
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80
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case 2: return a * b;
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81
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case 3: if (b != 0) return a / b;
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82
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}
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return 999999999;
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84
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}
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85
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```
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86
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switch文を使わないやり方も考えられます。
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87
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```Java
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88
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import java.util.Scanner;
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89
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90
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class Main {
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91
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public static void main(String[] args) {
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92
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Scanner sc = new Scanner(System.in);
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93
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System.out.println("4桁の数字を入力してください");
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94
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String number = sc.next();
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95
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int[] num = new int[4];
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96
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for (int i = 0; i < 4; i++) num[i] = number.charAt(i) - '0';
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System.out.println("計算値にしたい数字を入力してください");
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98
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int result = sc.nextInt();
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int[] op = new int[4];
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100
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Calc[] calc = { new Add(), new Sub(), new Mul(), new Div() };
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for (op[0] = 0; op[0] < 4; op[0]++) {
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int a = calc[op[0]].exec(num[0], num[1]);
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for (op[1] = 0; op[1] < 4; op[1]++) {
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int b = calc[op[1]].exec(a, num[2]);
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for (op[2] = 0; op[2] < 4; op[2]++)
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if (calc[op[2]].exec(b, num[3]) == result)
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print(num, op, result);
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}
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}
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}
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112
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private static void print(int[] num, int[] op, int result) {
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final String[] name = { "+", "-", "*", "/" };
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System.out.println(num[0] + name[op[0]] + num[1]
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+ name[op[1]] + num[2] + name[op[2]] + num[3] + " = " + result);
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}
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}
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118
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119
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class Calc { int exec(int a, int b) { return 0; } }
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120
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class Add extends Calc { int exec(int a, int b) { return a + b; } }
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121
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class Sub extends Calc { int exec(int a, int b) { return a - b; } }
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122
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class Mul extends Calc { int exec(int a, int b) { return a * b; } }
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123
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class Div extends Calc {
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124
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int exec(int a, int b) { return b != 0 ? a / b : 999999999; }
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125
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}
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126
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```
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