For the following problem I am trying to find maximum flow and minimum cut:

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I found the maximum flow as 6 like this:

$1-3-7-8:2 flows$

$1-2-5-8: 2 flows$

$1-3-4-5-8:1 flow$

$1-3-4-6-5-8:1 flow$

But I am having trouble to match the min cut, I thought it would be 8(by cutting the following arcs $(7,8)$ and $(5,8))$. How do I match the min cut? Or do you think I made a mistake finding max flow?


The maximum flow is $6$. To find a corresponding minimum cut, note that $S=\{1,3,4,7\}$ is the set of nodes reachable from the source node $1$ in the residual network. Now consider the arcs from $S$ to $N\setminus S$.

  • $\begingroup$ We took the following arcs, right? I am asking to make sure. (1-2),(4-5),(4-6),(7-8). $\endgroup$
    – diabolik
    Jan 22 at 21:43
  • $\begingroup$ Yes, those are correct, with sum of capacities equal to $2+1+1+2=6$, matching the flow value. $\endgroup$
    – RobPratt
    Jan 22 at 21:49

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