A min-heap that always hands back the smallest

When work arrives out of order but must be processed smallest-first — earliest deadline, closest timestamp, cheapest route — a heap beats re-sorting an array on every insert.

Implement a MinHeap class holding numbers. It is constructed with no arguments and starts empty. push(value) inserts a number and returns the new size. pop() removes and returns the smallest number currently held, or returns undefined when the heap is empty. peek() returns the smallest number without removing it, or undefined when empty. size() returns how many numbers are held.

Only the sequence of values coming out of pop() is specified; the internal arrangement is yours to choose. Duplicate values are allowed and each must come out separately.

What it has to do

• Repeated pop() calls return the values in ascending order.
• Duplicate values are each returned separately.
• peek() returns the smallest value without removing it.
• pop() and peek() return undefined on an empty heap.
• Pushing and popping can be interleaved in any order.

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