import java.util.Map.Entry;
public class Solution {
public List topKFrequent(int[] nums, int k) {
Map<Integer, Integer> map = new HashMap<>();
for(int i = 0; i < nums.length; i++) {
int key = nums[i];
if(!map.containsKey(key)) {
map.put(key, 1);
} else {
int val = map.get(key);
map.put(key, val+1);
}
}
Queue q = new PriorityQueue( new Comparator(){
@Override
public int compare(Integer i1, Integer i2){
if(map.get(i1)<map.get(i2)){
return 1;
}else if(map.get(i1)>map.get(i2)){
return -1;
}
return 0;
}
});
for(Map.Entry<Integer,Integer> val : map.entrySet()){
q.offer(val.getKey());
}
List res = new ArrayList<>();
int count=0;
while(count<k && !q.isEmpty()){
res.add(q.poll());
count++;
}
return res;
}
}
方法二：collection sort重写
————————————————————————————————————————
class Node implements Comparable {
int val;
int count;
public Node(int val, int count) {
this.val = val;
this.count = count;
}
public int compareTo(Node other) {
return other.count - this.count;
}
}
public List<Integer> topKFrequent(int[] nums, int k) {
List<Integer> res = new ArrayList<>();
if (nums == null || nums.length == 0 || k <= 0) return res;
Map<Integer, Node> map = new HashMap<>();
for (int num : nums) {
if (!map.containsKey(num)) map.put(num, new Node(num, 1));
else map.get(num).count += 1;
}
List<Node> list = new ArrayList<Node>(map.values());
Collections.sort(list);
for (int i = 0; i < k; i++) {
res.add(list.get(i).val);
}
return res;
}
Shawngbk
commented
7 years ago 
import java.util.Map.Entry; public class Solution { public List topKFrequent(int[] nums, int k) {
Map<Integer, Integer> map = new HashMap<>();
for(int i = 0; i < nums.length; i++) {
int key = nums[i];
if(!map.containsKey(key)) {
map.put(key, 1);
} else {
int val = map.get(key);
map.put(key, val+1);
}
}
Queue q = new PriorityQueue( new Comparator(){
@Override
public int compare(Integer i1, Integer i2){
if(map.get(i1)<map.get(i2)){
return 1;
}else if(map.get(i1)>map.get(i2)){
return -1;
}
return 0;
}
});
for(Map.Entry<Integer,Integer> val : map.entrySet()){
q.offer(val.getKey());
}
List res = new ArrayList<>();
int count=0;
while(count<k && !q.isEmpty()){
res.add(q.poll());
count++;
}
return res;
}
}
方法二：collection sort重写
————————————————————————————————————————
class Node implements Comparable {
int val;
int count;
public Node(int val, int count) {
this.val = val;
this.count = count;
}
public int compareTo(Node other) {
return other.count - this.count;
}
}