[BZOJ4653][Noi2016]区间

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <algorithm>
using namespace std;

int read() {
	int x = 0, f = 1; char c = getchar();
	while(!isdigit(c)){ if(c == ‘-‘) f = -1; c = getchar(); }
	while(isdigit(c)){ x = x * 10 + c - ‘0‘; c = getchar(); }
	return x * f;
}

#define maxi 500010
#define maxn 1000010
#define oo 2147483647

int n, m, num[maxn], cntn;
struct Interval {
	int l, r, len;
	Interval() {}
	Interval(int _1, int _2, int _3): l(_1), r(_2), len(_3) {}
	bool operator < (const Interval& t) const { return len < t.len; }
} ins[maxi];

int addv[maxn<<2], mxv[maxn<<2];
void pushdown(int o, int l, int r) {
	if(l == r || !addv[o]){ addv[o] = 0; return ; }
	int lc = o << 1, rc = lc | 1;
	addv[lc] += addv[o]; mxv[lc] += addv[o];
	addv[rc] += addv[o]; mxv[rc] += addv[o];
	addv[o] = 0;
	return ;
}
void update(int o, int l, int r, int ql, int qr, int v) {
	pushdown(o, l, r);
	if(ql <= l && r <= qr) {
		addv[o] += v; mxv[o] += v;
		return ;
	}
	int mid = l + r >> 1, lc = o << 1, rc = lc | 1;
	if(ql <= mid) update(lc, l, mid, ql, qr, v);
	if(qr > mid) update(rc, mid + 1, r, ql, qr, v);
	mxv[o] = max(mxv[lc], mxv[rc]);
	return ;
}
int query(int o, int l, int r) {
	pushdown(o, l, r);
	return mxv[o];
}

int main() {
	n = read(); m = read();
	for(int i = 1; i <= n; i++) {
		int l = read(), r = read();
		ins[i] = Interval(l, r, r - l);
		num[++cntn] = l; num[++cntn] = r;
	}
	
	sort(num + 1, num + cntn + 1);
	cntn = unique(num + 1, num + cntn + 1) - num - 1;
	for(int i = 1; i <= n; i++)
		ins[i].l = lower_bound(num + 1, num + cntn + 1, ins[i].l) - num,
		ins[i].r = lower_bound(num + 1, num + cntn + 1, ins[i].r) - num;
	sort(ins + 1, ins + n + 1);
	int l = 1, r, ans = oo;
	for(r = 1; r <= n; r++) {
		update(1, 1, cntn, ins[r].l, ins[r].r, 1);
		while(l <= r && query(1, 1, cntn) >= m) {
			ans = min(ans, ins[r].len - ins[l].len);
			update(1, 1, cntn, ins[l].l, ins[l].r, -1);
			l++;
		}
	}
	
	printf("%d\n", ans < oo ? ans : -1);
	
	return 0;
}