Tried to use stl lower_bound and upper_bound today and noticed that I didn’t quite understand them correctly before.

The corresponding leetcode problem

Some notes on these:

For std::lower_bound(T k), it returns the first element that is greater or equal to k.

For std::upper_bound(T k), it returns the first element that is greater than k.

For example:

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#include <algorithm>
#include <cassert>
#include <map>
#include <iostream>

using namespace std;

int main() {
    map<int, int> hm {{1, 1}, {3, 3}, {5, 5}, {7, 7}};
    map<int, int>::iterator it;
    // it == hm.end() because there does not exist a value in hm that is >= 8.
    it = hm.lower_bound(8);
    if(it == hm.end()) {
        cout << "Can't find a value >= 8..." << endl;
    } else {
        assert(0);
    }
    // it points to {7, 7}.
    it = hm.lower_bound(7);
    cout << "lower_bound for 7: " << it->first << endl;
    // it == hm.end() because there does not exist a value in hm that is > 7.
    it = hm.upper_bound(7);
    if(it == hm.end()) {
        cout << "Cannot find a value > 7..." << endl;
    } else {
        assert(0);
    }
    // it points to {5, 5}.
    it = hm.lower_bound(5);
    cout << "lower_bound for 5: " << it->first << endl;
    // it points to {7, 7}.
    it = hm.upper_bound(5);
    cout << "upper_bound for 5: " << it->first << endl;	
    return 0;
}

If we want to find a value in std::map that is strictly less than a given key k, we can do the following:

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auto it = hm.lower_bound(k);
if(it == hm.begin()) {
    cout << "Can't find a value that is strictly less than k!" << endl;
} else {
    --it;
    cout << "The value that is strictly less than k is: " << it->first << endl;
}

Note that if we provide custom comparator to std::map for example, we need to make sure that the comparator returns true only for the cases where lhs < rhs for std::lower_bound to work correctly. This is the same for std::upper_bound. ref

This is my github page, a place where I take notes on the stuff I learned from the courses I took and through-out my work.

Hexo is pretty easy to set up.

One problem I encounter is that when I run:

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$ hexo server

I got the following error:

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ERROR Local hexo not found

It turns out it’s because my node version is too low…

Everything works after I updated my node version.

When trying to deploy after adding a new post, the github page does not update.

It seems that a hexo clean is needed before running hexo depoly.

To start hexo server on a different port, use hexo server -p <port>.

Some useful links:

• https://gist.github.com/btfak/18938572f5df000ebe06fbd1872e4e39
• https://www.jianshu.com/p/42aa637f614a

Process of creating a blog:

• cd <path to blog/blog_init>
• hexo new post <title>
• hexo generate
• Use hexo server to check the generated page
• hexo deploy to deploy the change to github