POJ2376

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Cleaning Shifts

AC code

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#include <algorithm>
#include <cstdio>
#include <vector>
using namespace std;
typedef pair<int, int> ii;
/*
   1 5
   2 5
   3 6
 */
int main()
{
    int n, t;
    while (scanf("%d %d", &n, &t) == 2) {
        vector<ii> inp;
        for (int i = 0; i < n; i++) {
            int a, b;
            scanf("%d %d", &a, &b);
            inp.push_back(ii(a, b));
        }
        sort(inp.begin(), inp.end());
        int begin = 1, end = 0, ans = 1;
        for (int i = 0; i < n; i++) {
            if (inp[i].first <= begin || inp[i].second <= end) {
                // the starting point is <= begin or the ending point in less than the
                // current ending point
                if (inp[i].second > end) // extend the end point as far as you can
                    end = inp[i].second;
            } else {
                if (inp[i].first - end <= 1) // no gap between extended intervals
                    ans++;
                else {
                    ans = -1;
                    break;
                }
                begin = end + 1;
                i--;
            }
        }
        if (end < t) // crucial
            printf("-1\n");
        else
            printf("%d\n", ans);
    }
    return 0;
}