[Algorithm] How to use Max Heap to maintain K smallest items

Posted 2021-02-12

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Let???s say we are given an array:

[4,1,5,2,3,0,10]

We want to get K = 3 smallest items from the array and using Max heap data structure.

 

So this is how to think about it.

1. We take first K items put it into Max Heap:

     5

  /     

4          1

 

2. Then we move forward to next element ???2??? in the array, we check

• Whether 2 is smaller than current max item in heap, which is ???5???, if yes, then replace 5 with 2
• Then re-arrange the heap

     4

   /            

 2         1

3. Repeat the process for items [3,0]

     3????????????????????????2

   /                       /??????

 2         1              0????????????1

4. When the item is ???10??? which is larger than current max ???2???, we just ingore it.

5. In the end, we got K smallest items, we just need to print it out. (K smallest items are not ncessary in order)