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| #include <iostream>
#include <cstdio>
#include <algorithm>
#define maxn 1000010
#define maxm 25010
#define cn const node
using namespace std;
int n, m;
struct node {
int l, r, w, id;
friend bool operator < (cn &u, cn &v) { return u.w > v.w; }
} a[maxm];
int fa[maxn];
void init_fa() { for (int i = 1; i <= n + 1; ++i) fa[i] = i; }
int find(int x) { return x == fa[x] ? x : fa[x] = find(fa[x]); }
inline void merge(int l, int r) { while (l < r) l = fa[l] = find(l + 1); }
bool check(int x) {
init_fa();
for (int i = 1; i <= m; ++i) {
if (a[i].id > x) continue;
int L = a[i].l, R = a[i].r, l = a[i].l, r = a[i].r, w = a[i].w;
while (a[i + 1].w == w) { ++i;
if (a[i].id > x) continue;
L = max(L, a[i].l); l = min(l, a[i].l);
R = min(R, a[i].r); r = max(r, a[i].r);
}
if (L > R || find(L) >= R + 1) return 1;
merge(find(l), r + 1);
}
return 0;
}
int main() {
freopen("1.in", "r", stdin);
cin >> n >> m;
for (int i = 1; i <= m; ++i) scanf("%d%d%d", &a[i].l, &a[i].r, &a[i].w), a[i].id = i;
sort(a + 1, a + m + 1);
int l = 1, r = m, mid, ans = 0;
while (l <= r) {
mid = l + r >> 1;
if (check(mid)) ans = mid, r = mid - 1;
else l = mid + 1;
}
cout << ans << endl;
return 0;
}
|