[NOI2016]区间

将区间按照长度排序，每次将相同长度的区间插入，直到有一个点能被至少m个区间覆盖，这个可以用线段树维护。

这时我们就可以删除长度小的区间直到不满足条件。

重复做就可以了

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <map>
#define LL long long 

using namespace std;

inline LL read()
{
    LL x = 0, w = 1; char ch = 0;
    while(ch < '0' || ch > '9') {
        if(ch == '-') {
            w = -1;
        }
        ch = getchar();
    }
    while(ch >= '0' && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x * w;
}

const int MAXN = 5e5 + 10;

struct interval {
    int l, r;
    int len;
} inter[MAXN];

int ans = 2e9;
int N, M;
map<int, int> m;
int tmp[MAXN * 2];
int len;
int it[MAXN][3];
int cnt = 0;

bool cmp(interval a, interval b)
{
    return a.len < b.len;
}

struct segment {
    int maxn;
    int lazy;    
} seg[MAXN * 10];

void pushdown(int x)
{
    seg[x * 2].lazy += seg[x].lazy, seg[x * 2 + 1].lazy += seg[x].lazy;
    seg[x * 2].maxn += seg[x].lazy, seg[x * 2 + 1].maxn += seg[x].lazy;    
    seg[x].lazy = 0;
}

void pushup(int x)
{
    seg[x].maxn = max(seg[x * 2].maxn, seg[x * 2 + 1 ].maxn);
}

void update(int ul, int ur, int l, int r, int x, int k)
{
    if(ul <= l && ur >= r) {
        seg[x].maxn += k;
        seg[x].lazy += k;
        return;
    }
    int mid = (l + r) >> 1;
    pushdown(x);
    if(mid >= ul) {
        update(ul, ur, l, mid, x * 2, k);
    }
    if(mid < ur) {
        update(ul, ur, mid + 1, r, x * 2 + 1, k);
    }
    pushup(x);
    return;
}

int main()
{
    //cout<<sizeof seg / 1024 / 1024<<endl;
    //freopen("inter.in", "r", stdin);
    //freopen("iter.out", "w", stdout);
    N = read(), M = read();
    for(int i = 1; i <= N; i++) {
        tmp[i * 2 - 1] = inter[i].l = read(), tmp[i * 2] = inter[i].r = read();
        inter[i].len = inter[i].r - inter[i].l + 1;
    }
    sort(tmp + 1, tmp + 1 + 2 * N);
    len = unique(tmp + 1, tmp + 1 + 2 * N) - tmp - 1;
    //cout<<len<<endl;
    for(int i = 1; i <= len; i++) {
        m[tmp[i]] = i;
    }
    sort(inter + 1, inter + 1 + N, cmp);
    /*for(int i = 1; i <= N; i++) {
        cout<<m[inter[i].l]<<" "<<m[inter[i].r]<<endl;
    }
    cout<<endl;
    /*for(int i = 1; i <= len; i++) {
        cout<<tmp[i]<<" ";
    }
    cout<<endl;*/
    //return 0;
    inter[0].len = -1, inter[N + 1].len = 2e9;
    it[0][0] = 1e9;
    for(int i = 1; i <= N + 1; i++) {
        if(inter[i].len != inter[i - 1].len) {
            it[cnt][1] = i - 1;
            it[++cnt][0] = i;
            it[cnt][2] = inter[i].len;
        }
    }
    /*for(int i = 1; i <= cnt; i++) {
        cout<<it[i][0]<<" "<<it[i][1]<<" "<<it[i][2]<<endl;
    }
    cout<<endl;*/
    int mi = 0, ma = 0;
    int status = 0;
    while(mi <= cnt && ma < cnt) {
        while(seg[1].maxn < M && ma < cnt) {
            ma++;
            //cout<<ma<<endl;
            //cout<<it[ma][0]<<" "<<it[ma][1]<<endl;
            for(int i = it[ma][0]; i <= it[ma][1]; i++) {
                update(m[inter[i].l], m[inter[i].r], 1, len, 1, 1);
            }        
        }
        //cout<<ma<<" "<<seg[1].maxn<<endl;
        while(seg[1].maxn >= M) {
            ans = min(ans, it[ma][2] - it[mi][2]);
            for(int i = it[mi][0]; i <= it[mi][1]; i++) {
                update(m[inter[i].l], m[inter[i].r], 1, len, 1, -1);
            }
            mi++;
            //cout<<m[inter[219].l]<<" "<<m[inter[219].r]<<" "<<mi<<" "<<seg[1].maxn<<endl;
        }
        //cout<<mi<<endl;
    }
    if(ans == 2e9) {
        ans = -1;
    }
    printf("%d
", ans);
    return 0;
}