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.
找两个相等数的间距，间距最大为k，我的思路就是用map来保存index，看代码吧：）
class Solution { public: bool containsNearbyDuplicate(vector<int>& nums, int k) { int n = nums.size(); map<int, int> m; for (int i = 0; i < n; ++i) { if (m.find(nums[i]) != m.end()) { if (i - m[nums[i]] <= k) return true; else m[nums[i]] = i; } m[nums[i]] = i; } return false; } };