83 lines
2.5 KiB
Rust
83 lines
2.5 KiB
Rust
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// loj-101.rs
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use std::collections::VecDeque;
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#[derive(Clone, Copy, Debug)]
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struct Edge {
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to: usize,
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flow: i64,
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cap: i64,
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rev: usize,
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}
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struct Net(Vec<Vec<Edge>>, Vec<usize>, Vec<bool>);
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impl Net {
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fn new(n: usize) -> Self {
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Self(vec![vec![]; n+1], vec![0; n+1], vec![false; n+1])
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}
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fn add_edge(&mut self, from: usize, to: usize, cap: i64) {
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let to_edge = Edge {to, cap, flow: 0, rev: self.0[to].len()};
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self.0[from].push(to_edge);
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let from_edge = Edge {to: from, flow: 0, cap: 0, rev: self.0[from].len() - 1};
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self.0[to].push(from_edge);
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}
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fn bfs(&mut self, s: usize, t: usize) -> bool {
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self.1.fill(0);
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let mut dq = VecDeque::new();
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self.1[s] = 1;
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dq.push_back((s, 1));
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while let Some((v, l)) = dq.pop_front() {
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for e in &self.0[v] {
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if self.1[e.to] == 0 && e.cap > e.flow {
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self.1[e.to] = l + 1;
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dq.push_back((e.to, l + 1));
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}
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}
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}
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self.1[t] != 0
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}
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fn dfs(&mut self, s: usize, t: usize, cap: i64) -> i64 {
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if self.2[s] { return 0; }
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self.2[s] = true;
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if s == t { return cap; }
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let mut res = 0;
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let n = self.0[s].len();
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for i in 0..n {
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let e = self.0[s][i];
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if e.cap > e.flow && self.1[e.to] == self.1[s] + 1 {
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let new = self.dfs(e.to, t, (cap - res).min(e.cap - e.flow));
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self.0[s][i].flow += new;
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self.0[e.to][e.rev].flow -= new;
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res += new;
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if res == cap { return res; }
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}
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}
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res
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}
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fn max_flow(&mut self, s: usize, t: usize) -> i64 {
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let mut res = 0;
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while self.bfs(s, t) {
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self.2.fill(false);
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res += self.dfs(s, t, i64::MAX);
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}
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res
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}
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}
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fn main() {
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let mut buf = String::new();
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std::io::stdin().read_line(&mut buf).ok();
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let nmst: Vec<usize> = buf.trim().split(' ').map(|x|x.parse::<usize>().unwrap()).collect::<Vec<usize>>();
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let (n, m, s, t) = (nmst[0], nmst[1], nmst[2], nmst[3]);
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let mut net = Net::new(n);
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for _ in 0..m {
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buf.clear();
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std::io::stdin().read_line(&mut buf).ok();
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let uvc: Vec<i64> = buf.trim().split(' ').map(|x|x.parse::<i64>().unwrap()).collect::<Vec<i64>>();
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let (u, v, c) = (uvc[0] as usize, uvc[1] as usize, uvc[2]);
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net.add_edge(u, v, c);
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}
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println!("{}", net.max_flow(s, t));
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}
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