Add maxflow

Author: TonalidadeHidrica

src/maxflow.rs

@@ -1 +1,251 @@
+use crate::internal_queue::SimpleQueue;
+use std::cmp::min;
+use std::iter;
+use std::ops::{Add, AddAssign, Sub, SubAssign};
 
+// Maybe it should be in a separate module
+pub trait MfCapacity:
+    Copy + Ord + Add<Output = Self> + AddAssign + Sub<Output = Self> + SubAssign
+{
+    fn zero() -> Self;
+    fn max_value() -> Self;
+}
+
+impl MfCapacity for i32 {
+    fn zero() -> Self {
+        0
+    }
+    fn max_value() -> Self {
+        std::i32::MAX
+    }
+}
+
+impl MfCapacity for i64 {
+    fn zero() -> Self {
+        0
+    }
+    fn max_value() -> Self {
+        std::i64::MAX
+    }
+}
+
+impl MfCapacity for u32 {
+    fn zero() -> Self {
+        0
+    }
+    fn max_value() -> Self {
+        std::u32::MAX
+    }
+}
+
+impl MfCapacity for u64 {
+    fn zero() -> Self {
+        0
+    }
+    fn max_value() -> Self {
+        std::u64::MAX
+    }
+}
+
+impl<Cap> MfGraph<Cap>
+where
+    Cap: MfCapacity,
+{
+    pub fn new(n: usize) -> MfGraph<Cap> {
+        MfGraph {
+            _n: n,
+            pos: Vec::new(),
+            g: iter::repeat_with(Vec::new).take(n).collect(),
+        }
+    }
+
+    pub fn add_edge(&mut self, from: usize, to: usize, cap: Cap) -> usize {
+        assert!(from < self._n);
+        assert!(to < self._n);
+        assert!(Cap::zero() < cap);
+        let m = self.pos.len();
+        self.pos.push((from, self.g[from].len()));
+        let rev = self.g[to].len();
+        self.g[from].push(_Edge { to, rev, cap });
+        let rev = self.g[from].len() - 1;
+        self.g[to].push(_Edge {
+            to: from,
+            rev,
+            cap: Cap::zero(),
+        });
+        m
+    }
+}
+
+struct Edge<Cap> {
+    from: usize,
+    to: usize,
+    cap: Cap,
+    flow: Cap,
+}
+
+impl<Cap> MfGraph<Cap>
+where
+    Cap: MfCapacity,
+{
+    fn get_edge(&self, i: usize) -> Edge<Cap> {
+        let m = self.pos.len();
+        assert!(i < m);
+        let _e = &self.g[self.pos[i].0][self.pos[i].1];
+        let _re = &self.g[_e.to][_e.rev];
+        Edge {
+            from: self.pos[i].0,
+            to: _e.to,
+            cap: _e.cap + _re.cap,
+            flow: _re.cap,
+        }
+    }
+    fn edges(&self) -> Vec<Edge<Cap>> {
+        let m = self.pos.len();
+        (0..m).map(|i| self.get_edge(i)).collect()
+    }
+    fn change_edge(&mut self, i: usize, new_cap: Cap, new_flow: Cap) {
+        let m = self.pos.len();
+        assert!(i < m);
+        assert!(Cap::zero() < new_flow && new_flow <= new_cap);
+        let (to, rev) = {
+            let _e = &mut self.g[self.pos[i].0][self.pos[i].1];
+            _e.cap = new_cap - new_flow;
+            (_e.to, _e.rev)
+        };
+        let _re = &mut self.g[to][rev];
+        _re.cap = new_flow;
+    }
+
+    pub fn flow(&mut self, s: usize, t: usize) -> Cap {
+        self.flow_with_capacity(s, t, Cap::max_value())
+    }
+    pub fn flow_with_capacity(&mut self, s: usize, t: usize, flow_limit: Cap) -> Cap {
+        let n_ = self._n;
+        assert!(s < n_);
+        assert!(t < n_);
+
+        let mut calc = FlowCalculator {
+            graph: self,
+            s,
+            t,
+            flow_limit,
+            level: vec![0; n_],
+            iter: vec![0; n_],
+            que: SimpleQueue::default(),
+        };
+
+        let mut flow = Cap::zero();
+        while flow < flow_limit {
+            calc.bfs();
+            if calc.level[t] == -1 {
+                break;
+            }
+            calc.iter.iter_mut().for_each(|e| *e = 0);
+            while flow < flow_limit {
+                let f = calc.dfs(t, flow_limit - flow);
+                if f == Cap::zero() {
+                    break;
+                }
+                flow += f;
+            }
+        }
+        flow
+    }
+
+    pub fn min_cut(&self, s: usize) -> Vec<bool> {
+        let mut visited = vec![false; self._n];
+        let mut que = SimpleQueue::default();
+        que.push(s);
+        while !que.empty() {
+            let &p = que.front();
+            que.pop();
+            visited[p] = true;
+            for e in &self.g[p] {
+                if e.cap != Cap::zero() && !visited[e.to] {
+                    visited[e.to] = true;
+                    que.push(e.to);
+                }
+            }
+        }
+        visited
+    }
+}
+
+struct FlowCalculator<'a, Cap> {
+    graph: &'a mut MfGraph<Cap>,
+    s: usize,
+    t: usize,
+    flow_limit: Cap,
+    level: Vec<i32>,
+    iter: Vec<usize>,
+    que: SimpleQueue<usize>,
+}
+
+impl<Cap> FlowCalculator<'_, Cap>
+where
+    Cap: MfCapacity,
+{
+    fn bfs(&mut self) {
+        self.level.iter_mut().for_each(|e| *e = -1);
+        self.level[self.s] = 0;
+        self.que.clear();
+        self.que.push(self.s);
+        while !self.que.empty() {
+            let v = *self.que.front();
+            self.que.pop();
+            for e in &self.graph.g[v] {
+                if e.cap == Cap::zero() || self.level[e.to] >= 0 {
+                    continue;
+                }
+                self.level[e.to] = self.level[v] + 1;
+                if e.to == self.t {
+                    return;
+                }
+                self.que.push(e.to);
+            }
+        }
+    }
+    fn dfs(&mut self, v: usize, up: Cap) -> Cap {
+        if v == self.s {
+            return up;
+        }
+        let mut res = Cap::zero();
+        let level_v = self.level[v];
+        for i in self.iter[v]..self.graph.g[v].len() {
+            self.iter[v] = i;
+            let &_Edge {
+                to: e_to,
+                rev: e_rev,
+                ..
+            } = &self.graph.g[v][i];
+            if level_v <= self.level[e_to] || self.graph.g[e_to][e_rev].cap == Cap::zero() {
+                continue;
+            }
+            let d = self.dfs(e_to, min(up - res, self.graph.g[e_to][e_rev].cap));
+            if d <= Cap::zero() {
+                continue;
+            }
+            self.graph.g[v][i].cap += d;
+            self.graph.g[e_to][e_rev].cap -= d;
+            res += d;
+            if res == up {
+                break;
+            }
+        }
+        return res;
+    }
+}
+
+#[derive(Default)]
+pub struct MfGraph<Cap> {
+    _n: usize,
+    pos: Vec<(usize, usize)>,
+    g: Vec<Vec<_Edge<Cap>>>,
+}
+
+struct _Edge<Cap> {
+    to: usize,
+    rev: usize,
+    cap: Cap,
+}