347.前K个高频元素

依旧快排，依旧选择，只是现在只需要确定频率前k不需要排到底

classSolution{publicint[]topKFrequent(int[]nums,intk){Map<Integer,Integer>map=newHashMap<>();List<int[]>list=newArrayList<>();int[]result=newint[k];for(inti=0;i<nums.length;i++){map.put(nums[i],map.getOrDefault(nums[i],0)+1);}map.forEach((ks,v)->{list.add(newint[]{ks,v});});kp(list,0,list.size()-1,k);for(inti=0;i<k;i++){result[i]=list.get(i)[0];}returnresult;}publicvoidkp(List<int[]>list,intstart,intend,intk){intindex=(int)(Math.random()*(end-start+1))+start;Collections.swap(list,start,index);intnum=list.get(start)[1],l=start-1,r=end+1;while(r>l){while(list.get(++l)[1]>num);while(list.get(--r)[1]<num);if(l>=r)break;Collections.swap(list,l,r);}if(r-start+1==k)return;if(r-start+1>k)kp(list,start,r,k);elsekp(list,r+1,end,k-r+start-1);}}