1 | /**
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2 | * Efficient array of booleans.
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3 | *
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4 | * The booleans are stored in an integer. Starting from the less significant bit up to
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5 | * the index {@link Selection#size()} the respective boolean is true iff the bit is 1.
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6 | *
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7 | * The values of all other bits are undefined.
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8 | */
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9 | public class Selection {
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10 | private int bits;
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11 | private int size;
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12 |
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13 | /**
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14 | * Create a selection
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15 | * @param size the size of the selection
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16 | * @param bits the values of the booleans encoded as integer
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17 | */
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18 | public Selection(int size, int bits)
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19 | {
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20 | setSize(size);
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21 | setBits(bits);
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22 | }
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23 |
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24 | /**
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25 | * Create a selection with all booleans set to false
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26 | *
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27 | * @param size the size of the selection. 0 <= size <= 32.
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28 | */
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29 | public Selection(int size)
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30 | {
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31 | setSize(size);
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32 | setBits(0);
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33 | }
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34 |
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35 | /**
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36 | * Set the boolean values
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37 | *
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38 | * @param bits the boolean values encoded as integer.
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39 | */
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40 | public void setBits(int bits)
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41 | {
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42 | this.bits = bits;
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43 | }
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44 |
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45 | /**
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46 | * Get the boolean values
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47 | *
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48 | * @return the boolean values encoded as integer.
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49 | */
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50 | public int bits()
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51 | {
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52 | return bits;
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53 | }
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54 |
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55 | /**
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56 | * Set the size of the selection.
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57 | *
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58 | * If the size is increased the values of the new booleans are undefined.
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59 | *
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60 | * @param size the new size of the selection. 0 <= size <= 32
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61 | */
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62 | public void setSize(int size)
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63 | {
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64 | if (size > 32) throw new IllegalArgumentException("a maximum of 32 bits is supported only");
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65 | if (size < 0) throw new IllegalArgumentException("the size must be greater or equal to zero");
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66 | this.size = size;
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67 | }
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68 |
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69 | /**
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70 | * Get the size of the selection
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71 | * @return the size of the selection
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72 | */
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73 | public int size()
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74 | {
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75 | return size;
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76 | }
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77 |
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78 | /**
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79 | * Set a boolean value
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80 | *
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81 | * @param index the index of the boolean
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82 | * @param value the value of the boolean
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83 | */
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84 | public void set(int index, boolean value)
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85 | {
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86 | if (index < 0 || index >= size) {
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87 | throw new IndexOutOfBoundsException();
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88 | }
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89 | if (value) {
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90 | int mask = 1 << index;
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91 | bits = bits | mask;
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92 | } else {
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93 | int mask = ~(1 << index);
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94 | bits = bits & mask;
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95 | }
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96 | }
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97 |
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98 | /**
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99 | * Get a boolean values
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100 | *
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101 | * @param index the index of the boolean
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102 | * @return the value of the selected boolean
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103 | */
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104 | public boolean get(int index)
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105 | {
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106 | if (index < 0 || index >= size) {
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107 | throw new IndexOutOfBoundsException();
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108 | }
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109 | int mask = 1 << index;
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110 | return (bits & mask) != 0;
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111 | }
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112 |
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113 | public String toString()
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114 | {
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115 | StringBuffer buf = new StringBuffer();
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116 | buf.append("[");
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117 | for (int i=0; i<size; i++) {
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118 | if (i != 0) buf.append(", ");
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119 | if (get(i)) {
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120 | buf.append("true");
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121 | } else {
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122 | buf.append("false");
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123 | }
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124 | }
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125 | buf.append("]");
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126 | return buf.toString();
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127 | }
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128 |
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129 | /**
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130 | * Calculates a selected sum
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131 | * @param addends a vector of integers. The vector must be as large as the selection.
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132 | * @return the sum of all addends for which the corresponding booleans are true.
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133 | */
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134 | public int sum(ArrayList<Integer> addends)
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135 | {
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136 | if (addends.size() != size()) throw new IllegalArgumentException("Not enough or too many addends");
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137 | int sum = 0;
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138 | for (int i=0; i<addends.size(); i++) {
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139 | if (get(i)) {
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140 | sum += addends.get(i);
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141 | }
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142 | }
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143 | return sum;
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144 | }
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145 | }
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