Task: Range consolidation
C: #include <stdio.h>
#include <stdlib.h>

typedef struct range_tag {
    double low;
    double high;
} range_t;

void normalize_range(range_t* range) {
    if (range->high < range->low) {
        double tmp = range->low;
        range->low = range->high;
        range->high = tmp;
    }
}

int range_compare(const void* p1, const void* p2) {
    const range_t* r1 = p1;
    const range_t* r2 = p2;
    if (r1->low < r2->low)
        return -1;
    if (r1->low > r2->low)
        return 1;
    if (r1->high < r2->high)
        return -1;
    if (r1->high > r2->high)
        return 1;
    return 0;
}

void normalize_ranges(range_t* ranges, size_t count) {
    for (size_t i = 0; i < count; ++i)
        normalize_range(&ranges[i]);
    qsort(ranges, count, sizeof(range_t), range_compare);
}



size_t consolidate_ranges(range_t* ranges, size_t count) {
    normalize_ranges(ranges, count);
    size_t out_index = 0;
    for (size_t i = 0; i < count; ) {
        size_t j = i;
        while (++j < count && ranges[j].low <= ranges[i].high) {
            if (ranges[i].high < ranges[j].high)
                ranges[i].high = ranges[j].high;
        }
        ranges[out_index++] = ranges[i];
        i = j;
    }
    return out_index;
}

void print_range(const range_t* range) {
    printf("[%g, %g]", range->low, range->high);
}

void print_ranges(const range_t* ranges, size_t count) {
    if (count == 0)
        return;
    print_range(&ranges[0]);
    for (size_t i = 1; i < count; ++i) {
        printf(", ");
        print_range(&ranges[i]);
    }
}

void test_consolidate_ranges(range_t* ranges, size_t count) {
    print_ranges(ranges, count);
    printf(" -> ");
    count = consolidate_ranges(ranges, count);
    print_ranges(ranges, count);
    printf("\n");
}

#define LENGTHOF(a) sizeof(a)/sizeof(a[0])

int main() {
    range_t test1[] = { {1.1, 2.2} };
    range_t test2[] = { {6.1, 7.2}, {7.2, 8.3} };
    range_t test3[] = { {4, 3}, {2, 1} };
    range_t test4[] = { {4, 3}, {2, 1}, {-1, -2}, {3.9, 10} };
    range_t test5[] = { {1, 3}, {-6, -1}, {-4, -5}, {8, 2}, {-6, -6} };
    test_consolidate_ranges(test1, LENGTHOF(test1));
    test_consolidate_ranges(test2, LENGTHOF(test2));
    test_consolidate_ranges(test3, LENGTHOF(test3));
    test_consolidate_ranges(test4, LENGTHOF(test4));
    test_consolidate_ranges(test5, LENGTHOF(test5));
    return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <utility>
#include <vector>



template <typename iterator>
void normalize_ranges(iterator begin, iterator end) {
    for (iterator i = begin; i != end; ++i) {
        if (i->second < i->first)
            std::swap(i->first, i->second);
    }
    std::sort(begin, end);
}



template <typename iterator>
iterator merge_ranges(iterator begin, iterator end) {
    iterator out = begin;
    for (iterator i = begin; i != end; ) {
        iterator j = i;
        while (++j != end && j->first <= i->second)
            i->second = std::max(i->second, j->second);
        *out++ = *i;
        i = j;
    }
    return out;
}

template <typename iterator>
iterator consolidate_ranges(iterator begin, iterator end) {
    normalize_ranges(begin, end);
    return merge_ranges(begin, end);
}

template <typename pair>
void print_range(std::ostream& out, const pair& range) {
    out << '[' << range.first << ", " << range.second << ']';
}

template <typename iterator>
void print_ranges(std::ostream& out, iterator begin, iterator end) {
    if (begin != end) {
        print_range(out, *begin++);
        for (; begin != end; ++begin) {
            out << ", ";
            print_range(out, *begin);
        }
    }
}

int main() {
    std::vector<std::pair<double, double>> test_cases[] = {
        { {1.1, 2.2} },
        { {6.1, 7.2}, {7.2, 8.3} },
        { {4, 3}, {2, 1} },
        { {4, 3}, {2, 1}, {-1, -2}, {3.9, 10} },
        { {1, 3}, {-6, -1}, {-4, -5}, {8, 2}, {-6, -6} }
    };
    for (auto&& ranges : test_cases) {
        print_ranges(std::cout, std::begin(ranges), std::end(ranges));
        std::cout << " -> ";
        auto i = consolidate_ranges(std::begin(ranges), std::end(ranges));
        print_ranges(std::cout, std::begin(ranges), i);
        std::cout << '\n';
    }
    return 0;
}