Andrei Alexandrescu, Research Scientist of Facebook, answered:

“First and foremost, the ideal Facebook engineering candidate should be good at coding.

We do care about one’s ability to code; code is quintessential for us, for engineers from front-end to back-end to system configurators to researchers.”

He gave an example. When you choose C/C++, a good warmup question is “Implement strstr()”.

The canonical solution looks like this:

char* strstr(char* haystack, char* needle) {
    for (;; ++haystack) {
        char* h = haystack;
        for (char* n = needle;; ++n, ++h) {
            if (!*n) return haystack;
            if (*h != *n) break;
        }
        if (!*h) return NULL;
    }
}

He also listed other requisites:

“The ideal Facebook engineer is a great hacker, a strong generalist (and in addition possibly exceptional depth in some area), and an adaptable person comfortable working in small, fluid teams.“

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