Find the k-th smallest element

sysu_strange

于 2015-11-25 16:48:54 发布

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本文介绍了一种算法用于在给定数组中找到第k+1小的元素，包括函数实现和具体示例。

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1001. Find the k-th smallest element

Given a sequence A=(a1,...,an), your job is to find the (k+1)-th smallest element of A.

For example, A=(3, 2, 3, 4, 5) and k=1, then 3 is returned, since 3 is the second smallest element of A.

Please implement and submit the following function:

int select(int a[], int n, int k) {

// Your code will be here. You may invoke other functions.

}

Note: 0<=k<n<=1000000

int select(int a[], int n, int k , int l = 0 ) {
    int pivot = a[l] ;
    int left = l + 1 , right = n - 1 ;
    while(left <= right){
        while(a[left] <= pivot){
            if(left > right) break ;
            left ++ ;
        }
        while(a[right] > pivot){
            if(left > right) break ;
            right -- ;
        }
        if(left > right) break ;
        swap(a[right] , a[left]) ;
    }
    swap(a[right] , a[l]) ;
    if(k == right) return a[right] ;
    if(k < right){
        return select(a , right , k , l) ;
    }else{
        return select(a , n, k , right + 1) ;
    }
}