[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[10001];
struct node
{
    int a, b;
}q[10001];

inline int read()
{
    int x = 0, f = 1;
    char ch = getchar();
    for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
    for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
    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 = 1; i <= n; i++)
    {
        q[i].a = read();
        q[i].b = read();
    }
    std::sort(q + 1, q + n + 1, cmp);
    for(i = 1; i <= n; i++)
    {
        max = 0;
        for(j = 1; j < i; j++)
            if(q[j].b < q[i].b)
                max = Max(max, f[j]);
        f[i] = max + 1;
        ans = Max(ans, f[i]);
    }
    printf("%d
", ans);
    return 0;
}