-
Notifications
You must be signed in to change notification settings - Fork 0
/
MCTS.js
182 lines (163 loc) · 5.55 KB
/
MCTS.js
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
import GameState from "./GameState.js"
import Node from "./Node.js"
export default class MCTS {
constructor(game, UBC1ExploreParam = 2) {
this.game = game
this.UBC1ExploreParam = UBC1ExploreParam
this.nodes = new Map()
}
/**
* Phase 1 of the MCTS algorithm.
* Selection: Select until node is not fully expanded or is terminal (leaf).
* @param {GameState} state
*/
select(state) {
let node = this.nodes.get(state.hash())
while(node.isFullyExpanded() && !node.isLeaf()) {
let plays = node.getAllPlays()
let bestPlay
let bestUCB1 = -Infinity
for(let play of plays) {
let childUCB1 = node.getChildNode(play).getUCB1Value(this.UBC1ExploreParam)
if(childUCB1 > bestUCB1) {
bestPlay = play
bestUCB1 = childUCB1
}
}
// select node with best ucb1 score
node = node.getChildNode(bestPlay)
//console.log("selected a node")
}
return node
}
/**
* Phase 2 of the MCTS algorithm.
* Expansion: Expand a random unexpanded child node.
* @param {Node} node
*/
expand(node) {
let unexpandedPlays = node.getUnexpandedPlays()
let index = Math.floor(Math.random() * unexpandedPlays.length)
let play = unexpandedPlays[index]
let childState = this.game.nextState(node.state, play)
let legalPlays = this.game.legalPlays(childState)
let childNode = node.expand(play, childState, legalPlays)
this.nodes.set(childState.hash(), childNode)
//console.log(childNode)
return childNode
}
/**
* Phase 3 of the MCTS algorithm.
* Simulation: Simulate a node to a terminal state, return winner.
* @param {Node} node
*/
simulate(node) {
let state = node.state.clone()
let winner = this.game.winner(state)
while(winner === false) {
let legalPlays = this.game.legalPlays(state)
let index = Math.floor(Math.random() * legalPlays.length)
let play = legalPlays[index]
state = this.game.nextState(state, play)
winner = this.game.winner(state)
//console.log(legalPlays)
}
return winner
}
/**
* Phase 4 of the MCTS algorithm.
* Backpropagation: Update ancestors statistics.
* @param {Node} node
* @param {Number} winner
*/
backpropagate(node, winner) {
while(node != null) {
node.n_plays++
// Update win counter when it was a win for the current player of the *node*!!!
if(node.state.player === winner) {
node.n_wins++
//console.log("win")
} else {
//console.log("no win")
}
node = node.parent
}
}
/**
* Create a node with the given state if not already existing.
* @param {GameState} state
*/
makeNode(state) {
if(!this.nodes.has(state.hash())) {
let unexpandedPlays = this.game.legalPlays(state)
let node = new Node(null, null, state, unexpandedPlays)
this.nodes.set(state.hash(), node)
}
}
/**
* From given state, repeatedly run MCTS to build statistics.
* @param {GameState} state
* @param {Number} timeout
*/
runSearch(state, timeout = 3) {
this.makeNode(state)
let end = Date.now() + timeout * 1000
while(Date.now() < end) {
let node = this.select(state)
//console.log(node)
//console.log(this.game.getFieldVisual(node.state))
let winner = this.game.winner(node.state)
//console.log(winner)
if(!node.isLeaf() && winner == false) {
node = this.expand(node)
winner = this.simulate(node)
console.log("AND THE WINNER IS: " + winner)
}
this.backpropagate(node, winner)
}
//console.log(this.nodes)
}
/**
* Get the best play from available statistics.
* @param {GameState} state
*/
bestPlay(state) {
this.makeNode(state)
let node = this.nodes.get(state.hash())
console.log(node)
if(node.isFullyExpanded() === false) throw new Error("Not enough statistics")
let allPlays = node.getAllPlays()
let bestPlay
let max = -Infinity
for(let play of allPlays) {
let childNode = node.getChildNode(play)
if(childNode.n_plays > max) {
bestPlay = play
max = childNode.n_plays
}
}
return bestPlay
}
/**
*
* @param {GameState} state
* @returns {Object} An object containing the current statistics.
*/
getStats(state) {
let node = this.nodes.get(state.hash())
let stats = { n_plays: node.n_plays,
n_wins: node.n_wins,
children: [] }
for (let child of node.children.values()) {
if (child.node === null)
stats.children.push({ play: child.play,
n_plays: null,
n_wins: null})
else
stats.children.push({ play: child.play,
n_plays: child.node.n_plays,
n_wins: child.node.n_wins})
}
return stats
}
}