gplib/include/gp/algorithms/partition.hpp

#pragma once
#include <gp/algorithms/move.hpp>

namespace gp {
    template<typename it_t, typename pred>
    it_t lomuto_partition(it_t first, it_t last, pred predicate = pred{}) {
        auto pivot = *--it_t(last);

        auto i = --it_t(first);
        
        for(auto j = first; j != last; ++j) {
            if(!predicate(*j, pivot)){
                ++i;
                gp::swap(*i, *j);
            }
        }

        return i;
    }

    template<typename it_t, typename pred>
    it_t hoare_partition(it_t first, it_t last, pred predicate = pred{}) {
        while(first != last) {
            while(predicate(*first)) {
                ++first;
                if(first == last) return first;
            }
            do {
                --last;
                if(first == last) return first;
            } while(!predicate(*last));

            swap(*first, *last);
            ++first;
        }
        return first;
    }

    
    template<typename it_t, typename pred>
    it_t partition(it_t first, it_t last, pred predicate = pred{}) {
        return gp::hoare_partition(first, last, predicate);
    }
}