min-cut.js

// Takes an adjacency list like:
//  { 1: [2, 3], 2: [1, 3], 3: [2, 1] } 

function pick(arr) {
  var idx = (arr.length * Math.random()) | 0;
  return arr[idx];
}

function remove(arr, el){
  var idx;
  while((idx = arr.indexOf(el)) > -1)
    arr.splice(idx, 1);
}

function minCut(graph) {
  var node, edge;
  while(Object.keys(graph).length > 2) {
    // pick a node
    node = pick(Object.keys(graph));
    // pick an edge
    edge = pick(graph[node]);
    // concat the array
    graph[node] = graph[node].concat(graph[edge]);
    // delete other vertex
    delete graph[edge];

    // update edges in other lists
    Object.keys(graph).forEach(function(it){
      var idx;
      while((idx = graph[it].indexOf(edge)) > -1) graph[it][idx] = node;
    });

    // remove self loops
    remove(graph[node], node);
  }

  return graph[Object.keys(graph)[0]].length;
}