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| #include <bits/stdc++.h>
#define N 1000005
using namespace std;
template <typename T>
inline void read(T &num) {
T x = 0, f = 1; char ch = getchar();
for (; ch > '9' || ch < '0'; ch = getchar()) if (ch == '-') f = -1;
for (; ch <= '9' && ch >= '0'; ch = getchar()) x = (x << 3) + (x << 1) + (ch ^ '0');
num = x * f;
}
int n, m, len[N], srt[N], mx;
struct intv {
int l, r;
} p[N];
bool cmp(intv x, intv y) { return x.r-x.l < y.r-y.l; }
void fCuCcFk() {
for (int i = 1; i <= n; i++) srt[++mx] = p[i].l, srt[++mx] = p[i].r;
sort(srt+1, srt+mx+1);
mx = unique(srt+1, srt+mx+1) - srt - 1;
for (int i = 1; i <= n; i++) {
len[i] = p[i].r - p[i].l + 1;
p[i].l = lower_bound(srt+1, srt+mx+1, p[i].l) - srt;
p[i].r = lower_bound(srt+1, srt+mx+1, p[i].r) - srt;
}
}
struct segtree {
int mx, tag;
} tr[N<<2];
void build(int ind, int l, int r) {
tr[ind].mx = tr[ind].tag = 0; if (l == r) return;
int mid = (l + r) >> 1;
build(ind<<1, l, mid); build(ind<<1|1, mid+1, r);
}
inline void pushdown(int ind) {
if (!tr[ind].tag) return; int v = tr[ind].tag; tr[ind].tag = 0;
tr[ind<<1].mx += v; tr[ind<<1].tag += v;
tr[ind<<1|1].mx += v; tr[ind<<1|1].tag += v;
}
void update(int ind, int l, int r, int x, int y, int v) {
if (x <= l && r <= y) {
tr[ind].mx += v; tr[ind].tag += v; return;
}
pushdown(ind); int mid = (l + r) >> 1;
if (x <= mid) update(ind<<1, l, mid, x, y, v);
if (mid < y) update(ind<<1|1, mid+1, r, x, y, v);
tr[ind].mx = max(tr[ind<<1].mx, tr[ind<<1|1].mx);
}
int main() {
read(n); read(m);
for (int i = 1; i <= n; i++) {
read(p[i].l); read(p[i].r);
}
sort(p + 1, p + n + 1, cmp);
fCuCcFk(); int ans = 0x3f3f3f3f;
build(1, 1, mx);
update(1, 1, mx, p[1].l, p[1].r, 1);
for (int i = 1, j = 1; i <= n; i++) {
while (j < n && tr[1].mx < m) {
j++;
update(1, 1, mx, p[j].l, p[j].r, 1);
}
if (tr[1].mx >= m) ans = min(ans, len[j] - len[i]);
update(1, 1, mx, p[i].l, p[i].r, -1);
}
printf("%d\n", ans == 0x3f3f3f3f ? -1 : ans);
return 0;
}
|
