Create dinic.py

graphs/dinic.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python2.7
+INF = float("inf")
+
+class Dinic:
+    def __init__(self, n):
+        self.lvl = [0] * n
+        self.ptr = [0] * n
+        self.q = [0] * n
+        self.adj = [[] for _ in range(n)]
+
+    def add_edge(self, a, b, c, rcap=0):
+        self.adj[a].append([b, len(self.adj[b]), c, 0])
+        self.adj[b].append([a, len(self.adj[a]) - 1, rcap, 0])
+
+    def dfs(self, v, t, f):
+        if v == t or not f:
+            return f
+
+        for i in range(self.ptr[v], len(self.adj[v])):
+            e = self.adj[v][i]
+            if self.lvl[e[0]] == self.lvl[v] + 1:
+                p = self.dfs(e[0], t, min(f, e[2] - e[3]))
+                if p:
+                    self.adj[v][i][3] += p
+                    self.adj[e[0]][e[1]][3] -= p
+                    return p
+            self.ptr[v] = self.ptr[v] + 1
+        return 0
+
+    def calc(self, s, t):
+        flow, self.q[0] = 0, s
+        for l in range(31):  # l = 30 maybe faster for random data
+            while True:
+                self.lvl, self.ptr = [0] * len(self.q), [0] * len(self.q)
+                qi, qe, self.lvl[s] = 0, 1, 1
+                while qi < qe and not self.lvl[t]:
+                    v = self.q[qi]
+                    qi += 1
+                    for e in self.adj[v]:
+                        if not self.lvl[e[0]] and (e[2] - e[3]) >> (30 - l):
+                            self.q[qe] = e[0]
+                            qe += 1
+                            self.lvl[e[0]] = self.lvl[v] + 1
+
+                p = self.dfs(s, t, INF)
+                while p:
+                    flow += p
+                    p = self.dfs(s, t, INF)
+
+                if not self.lvl[t]:
+                    break
+
+        return flow
+