SGU 133. Border 最小区间覆盖

题目链接点这儿

就是求最小区间覆盖的水题。已经被前面两道状压dp吓尿了，，，，

最小区间覆盖，贪心，将区间按照左端点排序，然后慢慢贪心即可。

#include <bits/stdc++.h>

#define up(i, lower, upper) for(int i = lower; i < upper; i++)
#define down(i, lower, upper) for(int i = upper-1; i >= lower; i--)

using namespace std;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef vector<int> vi;
typedef vector<pii> vpii;
typedef long long ll;
typedef unsigned long long ull;

const double pi = acos(-1.0);
const double eps = 1.0e-9;

template<class T>

inline bool read(T &n){
    T x = 0, tmp = 1; char c = getchar();
    while((c < '0' || c > '9') && c != '-' && c != EOF) c = getchar();
    if(c == EOF) return false;
    if(c == '-') c = getchar(), tmp = -1;
    while(c >= '0' && c <= '9') x *= 10, x += (c - '0'),c = getchar();
    n = x*tmp;
    return true;
}

template <class T>
inline void write(T n) {
    if(n < 0) {
        putchar('-');
        n = -n;
    }
    int len = 0,data[20];
    while(n) {
        data[len++] = n%10;
        n /= 10;
    }
    if(!len) data[len++] = 0;
    while(len--) putchar(data[len]+48);
}

///---------------------------------------------------------

struct node {
    int b, e;
    friend bool operator < (node a, node b) {
        if(a.b < b.b) return true;
        else if(a.b == b.b && a.e > b.e) return true;
        else return false;
    }
};

node a[20000];

int main() {
    int n;
    read(n);
    up(i, 0, n) read(a[i].b), read(a[i].e);
    sort(a, a+n);
    int cnt = 1, tail = a[0].e;
    up(i, 1, n) {
        if(tail <= a[i].e)
            tail = a[i].e, cnt++;
    }
    write(n - cnt); puts("");
}