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use std::collections::HashMap;
use crate::position::{Position, WIDTH, HEIGHT};
const COLUMNS_ORDER: [u64; 7] = [3, 2, 4, 1, 5, 0, 6];
pub fn solve(p: Position) -> i32 {
let mut cache = HashMap::with_capacity(30000);
solve_rec(p, -100000, 100000, &mut cache)
}
fn solve_rec(p: Position, a: i32, b: i32, cache: &mut HashMap<u64, i32>) -> i32 {
if let Some(score) = cache.get(&p.key()) {
return *score;
}
if p.is_draw() {
return 0;
}
for x in 0..WIDTH {
if p.is_valid_play(x) && p.is_winning_play(x) {
return (((WIDTH * HEIGHT + 1) as i32) - (p.play_count as i32)) / 2;
}
}
let mut alpha = a;
let mut beta = b;
let max = (((WIDTH * HEIGHT + 1) as i32) - (p.play_count as i32)) / 2;
if beta > max {
beta = max;
if alpha >= beta {
return beta;
}
}
for x_unordered in 0..(WIDTH as usize) {
let x = COLUMNS_ORDER[x_unordered];
if !p.is_valid_play(x) {
continue
}
let score = -solve_rec(p.play(x), -beta, -alpha, cache);
if score >= beta {
return score;
}
if score > alpha {
alpha = score;
}
}
cache.insert(p.key(), alpha);
return alpha;
}
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