Created
August 17, 2019 03:52
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class Heap { | |
constructor(comparator) { | |
this.elements = []; | |
this.end = -1; | |
this.cmp = comparator || ((a, b) => a - b); | |
} | |
getLeft(n) { | |
return (2 * (n + 1)) - 1; | |
} | |
getRight(n) { | |
return 2 * (n + 1); | |
} | |
getParent(n) { | |
return Math.floor((n - 1) / 2); | |
} | |
swap(i, j) { | |
const tmp = this.elements[i]; | |
this.elements[i] = this.elements[j]; | |
this.elements[j] = tmp; | |
} | |
heapify(pos) { | |
// assume the subtrees are valid heaps | |
// therefore we just swap if violating, and recurse | |
const lhs = this.getLeft(pos); | |
const rhs = this.getRight(pos); | |
let smallest = pos; | |
if (lhs <= this.end && | |
this.cmp(this.elements[smallest], this.elements[lhs]) > 0) { | |
smallest = lhs | |
} | |
if (rhs <= this.end && | |
this.cmp(this.elements[smallest], this.elements[rhs]) > 0) { | |
smallest = rhs | |
} | |
if (smallest != pos) { | |
// swap and heapify | |
this.swap(pos, smallest); | |
this.heapify(smallest); | |
} | |
} | |
push(e) { | |
let pos = ++this.end; | |
this.elements[pos] = e; | |
// swap with parent until heap condition is satisfied | |
while (true) { | |
if (this.cmp(this.elements[this.getParent(pos)], e) >= 0) { | |
this.swap(pos, this.getParent(pos)); | |
pos = this.getParent(pos); | |
} else { | |
break; | |
} | |
} | |
} | |
pop() { | |
if (this.end < 0) { | |
return undefined; | |
} | |
const output = this.elements[0]; | |
// move the last element to the front | |
this.elements[0] = this.elements[this.end]; | |
--this.end; | |
// heapify | |
this.heapify(0); | |
return output; | |
} | |
len() { | |
return this.end + 1; | |
} | |
} |
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