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a34a14054532
util/indexedbheap.lua

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util/indexedbheap.lua @ 6151:a34a14054532

util.indexedbheap: Fix a possible traceback when removing the last item.
author Waqas Hussain <waqas20@gmail.com>
date Wed, 23 Apr 2014 11:38:34 -0400
parent 5876:f62ad84811df
child 8382:e5d00bf4a4d5
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f62ad84811df util.indexedbheap: A priority queue implementation with a reverse index with no per-entry memory allocation.
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1
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2 local setmetatable = setmetatable;
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3 local math_floor = math.floor;
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4 local t_remove = table.remove;
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5
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6 local function _heap_insert(self, item, sync, item2, index)
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7 local pos = #self + 1;
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8 while true do
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9 local half_pos = math_floor(pos / 2);
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10 if half_pos == 0 or item > self[half_pos] then break; end
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11 self[pos] = self[half_pos];
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12 sync[pos] = sync[half_pos];
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13 index[sync[pos]] = pos;
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14 pos = half_pos;
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15 end
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16 self[pos] = item;
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17 sync[pos] = item2;
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18 index[item2] = pos;
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19 end
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21 local function _percolate_up(self, k, sync, index)
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22 local tmp = self[k];
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23 local tmp_sync = sync[k];
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24 while k ~= 1 do
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25 local parent = math_floor(k/2);
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26 if tmp < self[parent] then break; end
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27 self[k] = self[parent];
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28 sync[k] = sync[parent];
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29 index[sync[k]] = k;
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30 k = parent;
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31 end
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32 self[k] = tmp;
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33 sync[k] = tmp_sync;
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34 index[tmp_sync] = k;
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35 return k;
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36 end
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37
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38 local function _percolate_down(self, k, sync, index)
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39 local tmp = self[k];
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40 local tmp_sync = sync[k];
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41 local size = #self;
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42 local child = 2*k;
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43 while 2*k <= size do
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44 if child ~= size and self[child] > self[child + 1] then
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45 child = child + 1;
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46 end
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47 if tmp > self[child] then
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48 self[k] = self[child];
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49 sync[k] = sync[child];
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50 index[sync[k]] = k;
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51 else
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52 break;
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53 end
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54
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55 k = child;
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56 child = 2*k;
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57 end
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58 self[k] = tmp;
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59 sync[k] = tmp_sync;
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60 index[tmp_sync] = k;
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61 return k;
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62 end
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63
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64 local function _heap_pop(self, sync, index)
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65 local size = #self;
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66 if size == 0 then return nil; end
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67
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68 local result = self[1];
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69 local result_sync = sync[1];
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70 index[result_sync] = nil;
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71 if size == 1 then
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72 self[1] = nil;
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73 sync[1] = nil;
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74 return result, result_sync;
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75 end
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76 self[1] = t_remove(self);
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77 sync[1] = t_remove(sync);
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78 index[sync[1]] = 1;
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79
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80 _percolate_down(self, 1, sync, index);
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81
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82 return result, result_sync;
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83 end
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84
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85 local indexed_heap = {};
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86
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87 function indexed_heap:insert(item, priority, id)
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88 if id == nil then
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89 id = self.current_id;
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90 self.current_id = id + 1;
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91 end
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92 self.items[id] = item;
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93 _heap_insert(self.priorities, priority, self.ids, id, self.index);
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94 return id;
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95 end
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96 function indexed_heap:pop()
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97 local priority, id = _heap_pop(self.priorities, self.ids, self.index);
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98 if id then
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99 local item = self.items[id];
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100 self.items[id] = nil;
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101 return priority, item, id;
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102 end
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103 end
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104 function indexed_heap:peek()
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105 return self.priorities[1];
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106 end
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107 function indexed_heap:reprioritize(id, priority)
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108 local k = self.index[id];
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109 if k == nil then return; end
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110 self.priorities[k] = priority;
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111
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112 k = _percolate_up(self.priorities, k, self.ids, self.index);
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113 k = _percolate_down(self.priorities, k, self.ids, self.index);
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114 end
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115 function indexed_heap:remove_index(k)
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116 local result = self.priorities[k];
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117 if result == nil then return; end
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118
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119 local result_sync = self.ids[k];
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120 local item = self.items[result_sync];
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121 local size = #self.priorities;
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122
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123 self.priorities[k] = self.priorities[size];
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124 self.ids[k] = self.ids[size];
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125 self.index[self.ids[k]] = k;
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126
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127 t_remove(self.priorities);
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128 t_remove(self.ids);
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129
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130 self.index[result_sync] = nil;
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131 self.items[result_sync] = nil;
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132
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133 if size > k then
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134 k = _percolate_up(self.priorities, k, self.ids, self.index);
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135 k = _percolate_down(self.priorities, k, self.ids, self.index);
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136 end
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137
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138 return result, item, result_sync;
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139 end
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140 function indexed_heap:remove(id)
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141 return self:remove_index(self.index[id]);
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142 end
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143
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144 local mt = { __index = indexed_heap };
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145
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146 local _M = {
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147 create = function()
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148 return setmetatable({
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149 ids = {}; -- heap of ids, sync'd with priorities
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150 items = {}; -- map id->items
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151 priorities = {}; -- heap of priorities
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152 index = {}; -- map of id->index of id in ids
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153 current_id = 1.5
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154 }, mt);
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155 end
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156 };
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157 return _M;