51nod 1091 线段的重叠(贪心)

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<string>
#include<stack>
#include<queue>
#include<deque>
#include<set>
#include<vector>
#include<map>
#include<functional>
    
#define fst first
#define sc second
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,root<<1
#define rson mid+1,r,root<<1|1
#define lc root<<1
#define rc root<<1|1
#define lowbit(x) ((x)&(-x)) 

using namespace std;

typedef double db;
typedef long double ldb;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> PI;
typedef pair<ll,ll> PLL;

const db eps = 1e-6;
const int mod = 1e9+7;
const int maxn = 2e6+100;
const int maxm = 2e6+100;
const int inf = 0x3f3f3f3f;

int n;
struct node{
    int l, r;
};
node a[maxn];
bool cmp(node a, node b){
    if(a.l==b.l)return a.r > b.r;
    return a.l<b.l;
}
int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++){
        scanf("%d %d", &a[i].l,&a[i].r);
    }
    sort(a+1,a+1+n,cmp);
    int m = a[1].r;
    int ans = 0;
    for(int i = 2; i <= n; i++){
        if(m >= a[i].r){
            //覆盖
            ans = max(ans, a[i].r-a[i].l);
        }
        else{
            //相交、不想交
            ans = max(ans, m-a[i].l);
            m = a[i].r;
        }
    }
    printf("%d",ans);
    return 0;
}