JS中的优先级队列

Question

I am trying to use a priority Queue for my own data type which is a 3x3 array. The actual code and data type is more complex so I boiled it down to the essentials. Note that the priority queue works well for an integer data type (see output at the end). Everything is self explanatory. Assume the metric function returns a positive integer for a given 3X3 array. I am confused why the dequeueing from the heap does not return the min valued object (or max valued in case I got the comparator backwards but I got the middle value for both). For the data type of integer the priority Queue seems to work correctly as the output shows.

    var r = require('js-priority-queue');



    metric = function (A) {
    N =  A.length;
    if (A[0][1] == 0) return 123;
    if (A[0][1] == 5) return 124;
    if (A[0][1] == 1) return 122;
    if (A[0][1] == 6) return 122;
    return 0;
}


    mComparator = function (m1, m2) {
      ret = metric(m2) - metric(m1);
      return ret;
   }

   mHeap = new r(mComparator);

   nHeap = new r(function (a,b) {
      return b - a;
   })

   A = [[5, 0, 1], [7, 6, 3], [2, 4, 8]];
   B = [[5, 6, 1], [7, 0, 3], [2, 4, 8]];

   C = [[5, 1, 0], [7, 6, 3], [2, 4, 8]];
   D = [[0, 5, 1], [7, 6, 3], [2, 4, 8]];

   console.log("metric(A) -> %d", metric(A));
   console.log("metric(B) -> %d", metric(B));
   console.log("metric(C) -> %d", metric(C));
   console.log("metric(D) -> %d", metric(D));

   mHeap.queue(A);
   mHeap.queue(B);
   mHeap.queue(C);
   mHeap.queue(D);

   X = mHeap.dequeue();
   console.log(X);

   X = mHeap.dequeue();
   console.log(X);

   X = mHeap.dequeue();
   console.log(X);

   X = mHeap.dequeue();
   console.log(X);

   nHeap.queue(123);
   nHeap.queue(124);
   nHeap.queue(122);
   nHeap.queue(122);

   y = nHeap.dequeue();
   console.log(y);


#Output 
metric(A) -> 123
metric(B) -> 122
metric(C) -> 122
metric(D) -> 124
[ [ 5, 0, 1 ], [ 7, 6, 3 ], [ 2, 4, 8 ] ]
[ [ 0, 5, 1 ], [ 7, 6, 3 ], [ 2, 4, 8 ] ]
[ [ 5, 1, 0 ], [ 7, 6, 3 ], [ 2, 4, 8 ] ]
[ [ 5, 6, 1 ], [ 7, 0, 3 ], [ 2, 4, 8 ] ]
122

Answer 1

If you are using the adamhooper priority queue, then your problem is you are not supplying the comparator correctly. Change your constructor invocations to:

mHeap = new r({"comparator": mComparator});

nHeap = new r({"comparator": function (a,b) {
    return b - a;
}})

And you should start getting expected results. Note that this gives you max-heaps . Since you wanted min-heaps, you should also reverse your comparison order:

mComparator = function (m1, m2) {
    ret = metric(m1) - metric(m2);
    return ret;
}

mHeap = new r({"comparator": mComparator});

nHeap = new r({"comparator": function (a,b) {
    return a - b;
}})

Example code for correctly supplying a comparator is given on the github project's front page, but I see how it could be easy to miss.