快排、归并、堆排找第k大数

 

 

 

https://leetcode.cn/problems/kth-largest-element-in-an-array/

 

 

 

func findKthLargest(nums []int, k int) int {
    //quickPow(0,len(nums)-1,nums)
    //guibin(0,len(nums)-1,nums)
    // n:=len(nums)
    // return nums[n-k]
    return heatSort(k,nums)
}

//quickPow 快排
func quickPow(le,ri int,nums []int){
    if le>=ri{
       return
    }
    baseIndex:=findBase(le,ri,nums)
    quickPow(le,baseIndex-1,nums)
    quickPow(baseIndex+1,ri,nums)
}
func findBase(le,ri int,nums []int) int{
    base:=nums[le]
    for le<ri{
        for le<ri&&nums[ri]>=base{
            ri--
        }
        nums[le]=nums[ri]
        for le<ri&&nums[le]<base{
            le++
        }
        nums[ri]=nums[le]
    }
    nums[le]=base
    return le
}

// guibin 归并
func guibin(le,ri int,nums []int){
    if le>=ri{
        return
    }
    mid:=(le+ri)/2
    guibin(le,mid,nums)
    guibin(mid+1,ri,nums)
    mergeNums(le,mid,ri,nums)
}
func mergeNums(le,mid,ri int,nums []int){
    leBegin:=le;leEnd:=mid
    riBegin:=mid+1;riEnd:=ri
    tmp:=make([]int,0)
    for leBegin<=leEnd&&riBegin<=riEnd{
        if nums[leBegin]>nums[riBegin]{
            tmp=append(tmp,nums[riBegin])
            riBegin++
        }else{
            tmp=append(tmp,nums[leBegin])
            leBegin++
        }
    }
    for riBegin<=riEnd{
        tmp=append(tmp,nums[riBegin])
        riBegin++
    }
    for leBegin<=leEnd{
        tmp=append(tmp,nums[leBegin])
        leBegin++
    }
    for i:=range tmp{
        nums[le+i]=tmp[i]
    }
}


//堆排
var heap []int
func heatSort(k int,nums []int) int{
    heap=make([]int,0)
    for i:=range nums{
        heap=append(heap,nums[i])
        insertHeap()
    }
    
    for i:=1;i<k;i++{
        deleteHeap()
    }
    return heap[0]
}
func insertHeap(){
    now:=len(heap)-1
    for now>0{
        root:=(now-1)/2
        if heap[now]>=heap[root]{
            tmp:=heap[root]
            heap[root]=heap[now]
            heap[now]=tmp
            now=root
        }else{
            break
        }
    }
}
func deleteHeap(){
    n:=len(heap)-1
    if n<0{
        return
    }
    heap[0]=heap[n]
    now:=0
    for now*2+1<=n{
        le:=now*2+1
        ri:=now*2+2
        if ri>n||heap[le]>heap[ri]{
            if heap[le]>heap[now]{
                tmp:=heap[now]
                heap[now]=heap[le]
                heap[le]=tmp
                now=le
            }else{
                break
            }
        }else{
            if heap[ri]>heap[now]{
                tmp:=heap[now]
                heap[now]=heap[ri]
                heap[ri]=tmp
                now=ri
            }else{
                break
            }
        }
    }
    heap=heap[:n]
}