题目描述
Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.
Example 1:
Input: nums = [1,2,3,1], k = 3 Output: true
Example 2:
Input: nums = [1,0,1,1], k = 1 Output: true
Example 3:
Input: nums = [1,2,3,1,2,3], k = 2 Output: false
解法
暴力法
nums.size()和k都大的时候,时间复杂度为O(n2)
,运行超时。
class Solution {
public:
bool containsNearbyDuplicate(vector<int>& nums, int k) {
if(nums.empty()) return false;
for(int i=0;i<nums.size();i++){
for(int j=i+1;j<nums.size()&&j<=i+k;j++){
if(nums[i]==nums[j]) return true;
}
}
return false;
}
};
映射表
将前面k个数都存在hashtable中,每次查询当前元素是否在hashtable中。由于unordered_set底层基于hash
表实现,其插入、查找、删除时间复杂度为O(1)
,故算法整体时间复杂度O(n)
。
class Solution {
public:
bool containsNearbyDuplicate(vector<int>& nums, int k) {
if(nums.empty()) return false;
unordered_set<int> s;
for(int i=0;i<nums.size();i++){
if(s.find(nums[i])!=s.end()) return true;
s.insert(nums[i]);
if(s.size()>k) s.erase(nums[i-k]);
}
return false;
}
};