uva 10020 Minimal coverage (greedy)

uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=961

　　Classical greedy problem!

The Code: 

typedef pair<int, int> PII;
typedef vector<PII> VPII;
#define REP(i, n) for (int i = 0; i < (n); i++)

VPII rec, out;

void input() {
    rec.clear();
    int x, y;
    while (~scanf("%d%d", &x, &y) && (x || y)) rec.PB(MPR(x, y));
}

bool work(int n) {
    if (!SZ(rec)) return false;
    sort(ALL(rec));
    int mk = -1, L = 0;
    out.clear();
    REP(i, SZ(rec)) {
        if (rec[i].FI > L) {
            if (mk == -1 || (rec[mk].SE < rec[i].FI) && (rec[mk].SE < n)) return false;
            out.PB(rec[mk]);
            if (rec[mk].SE >= n) return true;
            L = rec[mk].SE;
            mk = i;
        }
        if (~mk) {
            if (rec[i].SE > rec[mk].SE) mk = i;
        } else mk = i;
    }
    if (rec[mk].SE >= n) {
        out.PB(rec[mk]);
        return true;
    }
    return false;
}

int main() {
    int n, T;
    scanf("%d", &T);
    while (T-- && ~scanf("%d", &n)) {
        input();
        if (work(n)) {
            printf("%d\n", SZ(out));
            REP(i, SZ(out)) printf("%d %d\n", out[i].FI, out[i].SE);
        } else {
            puts("0");
        }
        if (T) puts("");
    }
    return 0;
}

——written by Lyon