NlogN中最长的递增子序列长度。[了解算法]

问题陈述：目的是找到登录时间最长的递增子序列（不连续）。

算法：我理解算法，如下所述：http : //www.geeksforgeeks.org/longest-monotonically-increasing-subsequence-size-n-log-n/。

我不明白的是以下代码中存储在尾部的内容。

int LongestIncreasingSubsequenceLength(std::vector<int> &v) {
if (v.size() == 0)
    return 0;

std::vector<int> tail(v.size(), 0);
int length = 1; // always points empty slot in tail

tail[0] = v[0];
for (size_t i = 1; i < v.size(); i++) {
    if (v[i] < tail[0])
        // new smallest value
        tail[0] = v[i];
    else if (v[i] > tail[length-1])
        // v[i] extends largest subsequence
        tail[length++] = v[i];
    else
        // v[i] will become end candidate of an existing subsequence or
        // Throw away larger elements in all LIS, to make room for upcoming grater elements than v[i]
        // (and also, v[i] would have already appeared in one of LIS, identify the location and replace it)
        tail[CeilIndex(tail, -1, length-1, v[i])] = v[i];
}

return length;
}

例如，如果输入为{2,5,3，，11,8,10,13,6}，则代码给出正确的长度为6。但是尾部将存储2,3,6,8,10,13。

所以我想了解尾部存储了什么？这将有助于我理解该算法的正确性。