[luoguP2782] 友好城市（DP）

传送门

转化成 lis 后 n² 搞就行

——代码

 #include <cstdio>
 #include <iostream>
 #include <algorithm>

 int n, max, ans;
 int f[];
 struct node
 {
     int a, b;
 }q[];

 inline int read()
 {
     int x = , f = ;
     char ch = getchar();
     for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -;
     for(; isdigit(ch); ch = getchar()) x = (x << ) + (x << ) + ch - '';
     return x * f;
 }

 inline int Max(int x, int y)
 {
     return x > y ? x : y;
 }

 inline bool cmp(node x, node y)
 {
     return x.a < y.a;
 }

 int main()
 {
     int i, j, x, y;
     n = read();
     for(i = ; i <= n; i++)
     {
         q[i].a = read();
         q[i].b = read();
     }
     std::sort(q + , q + n + , cmp);
     for(i = ; i <= n; i++)
     {
         max = ;
         for(j = ; j < i; j++)
             if(q[j].b < q[i].b)
                 max = Max(max, f[j]);
         f[i] = max + ;
         ans = Max(ans, f[i]);
     }
     printf("%d\n", ans);
     return ;
 }