LeetCode219. Contains Duplicate II

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

思路：

我们使用multimap来存储num和其对应的下标，当第二次遇到时就可以直接计算两者之间的距离。

class Solution {
public:
	bool containsNearbyDuplicate(vector<int>& nums, int k) {
		multimap<int, int> num_pos;
		for (int i = 0; i<int(nums.size()); i++) {
			if (num_pos.find(nums[i]) == num_pos.end()) {
				num_pos.insert(make_pair(nums[i], i));
			}
			else {
				auto range = num_pos.equal_range(nums[i]);
				for (auto it = range.first; it != range.second; it++) {
					if (i - (*it).second <= k)
						return true;
				}
				num_pos.insert(make_pair(nums[i], i));
			}
		}
		return false;
	}
};