前往小程序,Get更优阅读体验!
立即前往
首页
学习
活动
专区
工具
TVP
发布
社区首页 >专栏 >Leetcode|Find K Closest Elements

Leetcode|Find K Closest Elements

作者头像
double
发布2018-04-02 17:17:23
7680
发布2018-04-02 17:17:23
举报
文章被收录于专栏:算法channel

01

题目

Given a sorted array, two integers k and x, find the k closest elements to x in the array. The result should also be sorted in ascending order. If there is a tie, the smaller elements are always preferred.

Input: [1,2,3,4,5], k=4, x=3 Output: [1,2,3,4]

Input: [1,2,3,4,5], k=4, x=-1Output: [1,2,3,4]

Note: The value k is positive and will always be smaller than the length of the sorted array. Length of the given array is positive and will not exceed 104 Absolute value of elements in the array and x will not exceed 104

题目的意思是求出与x最相近的k个元素

02

分析

考虑两种特殊情况:

  1. x 小于等于 arr[0]
  2. x 大于等于 arr[-1]

然后,考虑一般情况,这时与x的距离,分布情况为:与x的距离先降为0,然后再逐渐增大,所以里面又有两种可能:

  1. 距离等于0的元素个数大于或等于k
  2. 距离等于0的元素个数小于k,这种情况求解,稍微复杂,需要二分动态查找。

以上分析的时间复杂度为O(n),空间复杂度为O(1)。

03

python代码


代码语言:javascript
复制
"""
arr: array wanted to search
k : k numbers nearest to x
x: goal center point
assert:
  1. arr is sorted
  2. ele in arr is integer
"""
def findKNearestToX(arr=[1,3,5],k=2,x=0):
    # x less or equal than arr[0]
    if x <= arr[0]:
        return arr[:k]
    # x bigger or equal than arr[-1]
    if x >= arr[-1]:
        return arr[-k:]
    # ordinary cases: at least one zero,
    # distance distribution: decline-->0-->rise
    hi=0
    zerolen=0
    for i,item in enumerate(arr):
        item = abs(item-x)
        if item==0:
            hi=i
            zerolen+=1
            if zerolen == k:
                return arr[hi-zerolen+1:hi+1]
    # here shows: number of zero chunk is less than k
    # then it needs to dynamic binary search
    lo = hi - zerolen+1
    curlen = zerolen
    while curlen < k:
        if lo > 0 and abs(arr[lo-1]-x) <= abs(arr[hi+1]-x):
            lo-=1
        elif hi < len(arr):
            hi+=1
        curlen+=1
    return arr[lo:hi+1]

代码语言:javascript
复制
#单元test
#1
kNearest = findKNearestToX(arr=[1,3,5],k=2,x=0)
#2
kNearest = findKNearestToX(arr=[1,3,5],k=2,x=5)
#3
#3-1
kNearest = findKNearestToX(arr=[1,3,3,3,5],k=2,x=3)
#3-2
kNearest = findKNearestToX(arr=[1,3,4,5],k=3,x=3)
#3-3
kNearest = findKNearestToX(arr=[-1,3,4,4],k=3,x=3)
print(kNearest)
本文参与 腾讯云自媒体同步曝光计划,分享自微信公众号。
原始发表:2018-01-11,如有侵权请联系 cloudcommunity@tencent.com 删除

本文分享自 程序员郭震zhenguo 微信公众号,前往查看

如有侵权,请联系 cloudcommunity@tencent.com 删除。

本文参与 腾讯云自媒体同步曝光计划  ,欢迎热爱写作的你一起参与!

评论
登录后参与评论
0 条评论
热度
最新
推荐阅读
领券
问题归档专栏文章快讯文章归档关键词归档开发者手册归档开发者手册 Section 归档