POJ1716 Integer Intervals

URL: http://poj.org/problem?id=1716

Description

An integer interval [a,b], a < b, is a set of all consecutive integers beginning with a and ending with b.
Write a program that: finds the minimal number of elements in a set containing at least two different integers from each interval.

Input

The first line of the input contains the number of intervals n, 1 <= n <= 10000. Each of the following n lines contains two integers a, b separated by a single space, 0 <= a < b <= 10000. They are the beginning and the end of an interval.

Output

Output the minimal number of elements in a set containing at least two different integers from each interval.

Sample Input

43 62 40 24 7

Sample Output

4

      各区间以未尾元素的大小排序；求解过程中，若某个区间内包含已选出整数的个数不足两个，则要又要选出新的整数，此时选取该区间最靠后的元素，这样能尽量使后面的区间在包含最大程度上包含新选的整数。

       代码如下：

#include <cstdio>#include <algorithm>struct interval{    int a;    int b;};bool cmp(interval x,interval y){    return x.b < y.b;}int main(){    int n, s, e, ans;    scanf("%d", &n);     interval v[n];    for(int i = 0; i < n; i++)         scanf("%d %d", &v[i].a, &v[i].b);    std::sort(v, v + n, cmp);    e = v[0].b; s = e - 1; ans = 2;    for(int i = 1; i < n; i++){        if(e < v[i].a){            ans += 2; e = v[i].b; s = e-1;        }        else if(s < v[i].a){            ans += 1; s = e; e = v[i].b;       }    }    printf("%d\n", ans);    return 0;}