Find the K smallest numbers in an unsorted integer array A. The returned numbers should be in ascending order.
Assumptions
- A is not null
- K is >= 0 and smaller than or equal to size of A
Return
- an array with size K containing the K smallest numbers in ascending order
Examples
-
A = {3, 4, 1, 2, 5}, K = 3, the 3 smallest numbers are {1, 2, 3}
public class Solution {
// use a priority queue(max heap with size of k) to figure it out.
// we traverse the array one time, whenever we met a element, we check it if smaller then the top element of the heap
// if it is, we poll and insert that new element in
// if it isn't, we do nothing
// time: O(n)
// space: O(k)
//
// thing to konw better: the vanilla priority q in java is max heap or min heap?
// how to turn a priority q into a array or a list in a efficient way?
//
// assumption: all element in array is integer and small than Integer.MAX_VALUE and larger than Integer.MIN_VALUE
// array is not null, array's length can be 0
// k can be zero, k is not larger than the length of array
public int[] kSmallest(int[] array, int k) {
// Write your solution here
int[] res = new int[k];
if(k==0){
return res;
}
PriorityQueue<Integer> pq = new PriorityQueue<>(k,Collections.reverseOrder());
for(int i=0; i<array.length; i++){
if(pq.size()<k){
pq.offer(array[i]);
}else{
if(array[i]<pq.peek()){
pq.poll();
pq.offer(array[i]);
}
}
}
for(int i=0; i<k; i++){
res[k-i-1] = pq.poll();
}
return res;
}
}
来源：https://www.cnblogs.com/zg1005/p/12131315.html