最小的K个数

最小的K个数（分割）

size_t Partition(vector<int> &arr, size_t left, size_t right)

{

int data=arr[left];

while(left<right)

{

while(left<right&&data<=arr[right]) right--;

arr[left]=arr[right];

while(left<right&&data>arr[left]) left++;

arr[right]=arr[left];

}

 

arr[left]=data;

return left;

}

void FindMinK(vector<int> &arr, size_t k)

{

assert(k>0&&arr.size()>k);

size_t left, right, mind;

 

for(left=0,right=arr.size()-1;left<right;)

{

mind = Partition(arr, left, right);

if(mind==k) return;

 

mind < k?(left=mind+1):(right=mind-1);

}

}

最小的K个数（堆）

void HeapAdjust(vector<int> &arr, size_t start)

{

int tmp=arr[start];

size_t child=2*start+1;

size_t end=arr.size()-1;

 

while(child <= end)

{

if(child<end && arr[child]<arr[child+1]) child++;

 

if(arr[child]>tmp)

{

arr[start]=arr[child];

 

start=child;

child=2*start+1;

}

else

break;

}

 

arr[start] = tmp;

}

 

void FindMinK(vector<int> &arr, vector<int>& bigHeap, size_t k)

{

assert(arr.size() > k && k > 0);

bigHeap.resize(k);

 

for (int i = 0; i < bigHeap.size(); i++)

{

bigHeap[i] = arr[i];

}

 

for(int i=bigHeap.size()/2;i>=0;i--)

{

HeapAdjust(bigHeap, i);

}

 

for (int i = bigHeap.size(); i < arr.size(); i++)

{

if (bigHeap[0] > arr[i])

{

bigHeap[0] = arr[i];

HeapAdjust(bigHeap, 0);

}

}

}