P1496 火烧赤壁

#include <bits/stdc++.h>
using namespace std;
const int maxn = 20005;
int n;
int sum = 0;
int a[maxn], b[maxn];
int main()
{
  cin >> n;
  for (int i = 0; i < n; i++)
  {
    cin >> a[i] >> b[i];
  }
  sort(a, a + n);
  sort(b, b + n);
  for (int i = 0; i < n; i++)
  {
    sum += b[i] - a[i];
    if (i + 1 < n)
    { // 不是最后一条线段
      if (b[i] > a[i + 1])
      { // 与后一条线段有重复
        sum -= (b[i] - a[i + 1]);
      }
    }
  }
  cout << sum;
}