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#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
#include <climits>
#include <cmath>
#include <cassert>
#include "ai_mcts.h"
static int mcts_niterations = 5000;
// static int mcts_niterations = 5000;
static int mcts_newnode_playouts = 3;
static int playout(Board &bd, int player) {
Move poss[N * N * N];
while (true) {
int nposs = 0;
int winidx = -1;
bd.forEachMove(player, [&bd, &poss, &nposs, &winidx, player](Move mv) {
Board bd2 = bd;
int win = bd2.applyCW(mv);
if (win * player >= 0) {
poss[nposs++] = mv;
if (win != 0) {
winidx = nposs - 1;
return true;
}
}
return false;
});
if (nposs == 0) return -player;
int index = winidx == -1 ? rand() % nposs : winidx;
int win = bd.applyCW(poss[index]);
if (win != 0) return win;
player = -player;
}
}
struct Node {
int nwin = 0, ntotal = 0; // nwin: number of wins, as regarded from the player on turn after the parent node
bool terminal = false; // someone has won
Move inedge;
Node *parent;
vector<Node> children;
bool allExpanded = false;
};
static float scoreFormula(const Node &node) {
return (float)node.nwin / node.ntotal + sqrtf(2.0f * logf(node.parent->ntotal) / node.ntotal);
}
static Node& nodeSelect(Node &from, Board *bd, int *onturn) {
if (!from.allExpanded) return from;
assert(from.children.size() != 0);
float maxscore = -1;
Node *choice = nullptr;
for (Node &ch : from.children) {
float score = scoreFormula(ch);
if (score > maxscore) {
maxscore = score;
choice = &ch;
}
}
bd->apply(choice->inedge);
if (choice->terminal) {
return *choice;
}
*onturn = -*onturn;
return nodeSelect(*choice, bd, onturn);
}
static Node& expand(Node &from, const Board &bd, int onturn) {
if (from.terminal) {
from.ntotal += mcts_newnode_playouts;
if (from.nwin > 0) {
from.nwin += from.ntotal;
}
return from;
}
assert(!from.allExpanded);
if (from.children.size() == 0) {
// cerr << " expand: initialising children" << endl;
bd.forEachMove(onturn, [&from, &bd](Move mv) {
from.children.emplace_back();
Node &ch = from.children.back();
ch.inedge = mv;
ch.parent = &from;
return false;
});
}
vector<int> poss;
poss.reserve(from.children.size());
for (int i = 0; i < (int)from.children.size(); i++) {
if (from.children[i].ntotal == 0) {
poss.push_back(i);
}
}
assert(poss.size() != 0);
int index = poss[rand() % poss.size()];
// cerr << " expand: poss.size()=" << poss.size() << " index=" << index << " f.c[i].nt=" << from.children[index].ntotal << endl;
if (poss.size() == 1) from.allExpanded = true;
Node &node = from.children[index];
Board bd2 = bd;
int win = bd2.applyCW(node.inedge);
if (win != 0) {
node.terminal = true;
node.nwin = mcts_newnode_playouts * (win == onturn);
node.ntotal = mcts_newnode_playouts;
return node;
}
for (int i = 0; i < mcts_newnode_playouts; i++) {
Board bd3 = bd2;
win = playout(bd3, onturn);
node.nwin = win == onturn;
}
node.ntotal = mcts_newnode_playouts;
return node;
}
static void backPropagate(Node &node, int propWins, int propTotal) {
node.nwin += propWins;
node.ntotal += propTotal;
if (node.parent == nullptr) return;
backPropagate(*node.parent, propTotal - propWins, propTotal);
}
static string incrementalFilename() {
static int i = 1;
return "tree_" + to_string(i++) + ".dot";
}
static void writeTreeNode(const Node &node, ostream &stream, int maxdepth) {
stream << "\"" << &node << "\" [label=\"" << node.nwin << "/" << node.ntotal << "\\n" << node.inedge << "\"];\n";
if (maxdepth <= 0) return;
vector<const Node*> nexts;
nexts.reserve(node.children.size());
for (const Node &ch : node.children) {
nexts.push_back(&ch);
}
sort(nexts.begin(), nexts.end(), [](const Node *a, const Node *b) {
return a->ntotal < b->ntotal;
});
for (const Node *ch : nexts) {
stream << "\"" << &node << "\" -> \"" << ch << "\";\n";
writeTreeNode(*ch, stream, maxdepth - 1);
}
}
static void writeTree(const Node &root, const string &filename, int maxdepth = 1) {
ofstream f(filename);
assert(f);
f << "digraph G {\n";
writeTreeNode(root, f, maxdepth);
f << "}\n";
f.close();
cerr << "Wrote tree to \"" << filename << "\"" << endl;
}
Move AI::MCTS::findMove(const Board &bd, int player) {
Node root;
root.inedge = Move(-1, -1);
root.parent = nullptr;
for (int iter = 0; iter < mcts_niterations; iter++) {
// cerr << "ITERATION " << iter << " root.ntotal = " << root.ntotal << endl;
Board bd2 = bd;
int onturn = player;
Node &node = nodeSelect(root, &bd2, &onturn);
// cerr << "Selected " << &node << endl;
Node &newnode = expand(node, bd2, onturn);
// cerr << "Expanded " << &newnode << endl;
backPropagate(node, newnode.ntotal - newnode.nwin, newnode.ntotal);
}
int maxtotal = -1;
Move maxat;
for (const Node &node : root.children) {
if (node.ntotal > maxtotal) {
maxtotal = node.ntotal;
maxat = node.inedge;
}
}
// writeTree(root, incrementalFilename());
return maxat;
}
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