Classical greedy problem!

The Code: 

1 typedef pair
      
        PII; 2 typedef vector
       
         VPII; 3 #define REP(i, n) for (int i = 0; i < (n); i++) 4  5 VPII rec, out; 6  7 void input() { 8     rec.clear(); 9     int x, y;10     while (~scanf("%d%d", &x, &y) && (x || y)) rec.PB(MPR(x, y));11 }12 13 bool work(int n) {14     if (!SZ(rec)) return false;15     sort(ALL(rec));16     int mk = -1, L = 0;17     out.clear();18     REP(i, SZ(rec)) {19         if (rec[i].FI > L) {20             if (mk == -1 || (rec[mk].SE < rec[i].FI) && (rec[mk].SE < n)) return false;21             out.PB(rec[mk]);22             if (rec[mk].SE >= n) return true;23             L = rec[mk].SE;24             mk = i;25         }26         if (~mk) {27             if (rec[i].SE > rec[mk].SE) mk = i;28         } else mk = i;29     }30     if (rec[mk].SE >= n) {31         out.PB(rec[mk]);32         return true;33     }34     return false;35 }36 37 int main() {38     int n, T;39     scanf("%d", &T);40     while (T-- && ~scanf("%d", &n)) {41         input();42         if (work(n)) {43             printf("%d\n", SZ(out));44             REP(i, SZ(out)) printf("%d %d\n", out[i].FI, out[i].SE);45         } else {46             puts("0");47         }48         if (T) puts("");49     }50     return 0;51 }
       
      

 

——written by Lyon