Leetcode175: Contains Duplicate III

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between i and j is at most k.

class Solution {
public:
    bool containsNearbyAlmostDuplicate(vector& nums, int k, int t) {
        map m;
        int j = 0;
        for (int i = 0; i < nums.size(); ++i) {
            if (i - j > k && m[nums[j]] == j) m.erase(nums[j++]);
            auto a = m.lower_bound(nums[i] - t);
            if (a != m.end() && abs(a->first - nums[i]) <= t) return true;
            m[nums[i]] = i;
        }
        return false;
    }
};