Get number of K-Large

1. Using a quick sort, randomly finding an element x from an array, dividing the array into two parts that are smaller than x and larger than X, assuming that the number of elements smaller than x is B, then:

(1) if B >= K, then recursion from the small part of the x to find the element K large.

(2) If B < K, then recursively find the larger element (K-b) from the larger part of X.

2.

(1) Using the minimum heap, similar to the O (NLOGM) algorithm in the written question.

(2) Use the maximum heap, similar to the O (MLOGN) algorithm in the written question.

　

intGetParentintBeginintEndintindex) {    intParentindex = (index-begin-1)/2+begin; returnParentindex;}intGetlchild (intBeginintEndintindex) {    intLchildindex = (index-begin) *2+1+begin; returnLchildindex;}intGetrchild (intBeginintEndintindex) {    intRchildindex = (index-begin) *2+1+ Begin +1; returnRchildindex;}voidAdjustheap (vector<int> & V,intBeginintEndintindex) {    intLchild =Getlchild (Begin,end,index); intRchild =Getrchild (Begin,end,index); intlargest =index; if(Rchild <= end && V[rchild] >V[largest]) largest=Rchild; if(Lchild <= end && V[lchild] >V[largest]) largest=Lchild; if(Largest! =index) {        inttemp =V[largest]; V[largest]=V[index]; V[index]=temp;    Adjustheap (v,begin,end,largest); }//Show (v,begin,end);}voidBuildmaxheap (vector<int> & V,intBeginintend) {    intParent =GetParent (begin,end,end);  while(Parent >=begin)        {adjustheap (v,begin,end,parent); Parent--; }}voidHeapsort (vector<int> & V,intBeginintend) {buildmaxheap (v,begin,end);//Show (v,begin,end);    intTempend =end;  for(; Tempend >begin;) {        inttemp =V[begin]; V[begin]=V[tempend]; V[tempend]=temp; Adjustheap (V,begin,--tempend,begin); }}intGetkmaxbyheapsort (vector<int> & V,intBeginintEndintK)    {//This is similar to the complete heap sequencing step, but the number of step cycles has decreased by buildmaxheap (v,begin,end); inti =0 ; inttemp =0;  for(; i < K; i++) {Temp=V[begin]; V[begin]=V[end]; V[end]=temp; Adjustheap (V,begin,--end,begin); }    returntemp;}

Like a quick sort of way

intPartition (vector<int> & V,intBeginintend) {    intKey =V[begin]; inti =begin; intj =end;  while(i<j) {         while(J>i && V[j] <=key) J--;  while(J>i && V[i] >key) I++; inttemp =V[j]; V[J]=V[i]; V[i]=temp; } V[i]=key; returni;}voidQuicksort (vector<int> & V,intBeginintend) {    if(Begin <end) {        intMID =partition (V,begin,end); Quicksort (V,begin,mid-1); Quicksort (V,mid+1, end); }}intGetkmaxbyquicksort (vector<int> & V,intBeginintEndintK) {    if(Begin = =end)returnV[begin]; intMID =partition (V,begin,end); intnum = Mid-begin +1; if(num = =K) {        returnV[begin +K]; }    if(Num >K) {        returnGetkmaxbyquicksort (v,begin,mid-1, K); }    if(Num <K) {            returnGetkmaxbyquicksort (v,mid+1, end,k-num); }}

Get number of K-Large