Submission #993792

#	Time	Username	Problem	Language	Result	Execution time	Memory
993792		TimDee	Railway (BOI17_railway)	C++17	100 / 100	74 ms	19372 KiB

railway

    // I solved this problem in contest (it appeared on our TST2024), but i'm too lazy to code it again, so it's a copy of rainboy's submission.
        #include <stdio.h>
        #include <stdlib.h>
        #define N	100000

unsigned X=12345; int rand_() {return (X*=3)>>1;}
         
        int ij[N];
        int *eh[N], eo[N];
         
        void append(int i, int j) {
        	int o = eo[i]++;
         
        	if (o >= 2 && (o & o - 1) == 0)
        		eh[i] = (int *) realloc(eh[i], o * 2 * sizeof *eh[i]);
        	eh[i][o] = j;
        }
         
        int dd[N], pp[N], qq[N], ff[N], sz[N], ta[N], tb[N], qu[N], cnt;
         
        void dfs(int p, int f, int i, int d) {
        	int o, j_;
         
        	qu[ta[i] = cnt++] = i;
        	dd[i] = d, pp[i] = p, ff[i] = f;
        	j_ = -1, sz[i] = 1;
        	for (o = 0; o < eo[i]; o++) {
        		int h = eh[i][o], j = i ^ ij[h];
         
        		if (h != f) {
        			dfs(i, h, j, d + 1);
        			if (j_ == -1 || sz[j_] < sz[j])
        				j_ = j;
        			sz[i] += sz[j];
        		}
        	}
        	if (j_ != -1)
        		qq[j_] = -1;
        	tb[i] = cnt;
        }
         
        int lca(int i, int j) {
        	while (qq[i] != qq[j])
        		if (dd[qq[i]] > dd[qq[j]])
        			i = pp[qq[i]];
        		else
        			j = pp[qq[j]];
        	return dd[i] < dd[j] ? i : j;
        }
         
        void sort(int *ii, int l, int r) {
        	while (l < r) {
        		int i = l, j = l, k = r, i_ = ii[l + rand_() % (r - l)], tmp;
         
        		while (j < k)
        			if (ta[ii[j]] == ta[i_])
        				j++;
        			else if (ta[ii[j]] < ta[i_]) {
        				tmp = ii[i], ii[i] = ii[j], ii[j] = tmp;
        				i++, j++;
        			} else {
        				k--;
        				tmp = ii[j], ii[j] = ii[k], ii[k] = tmp;
        			}
        		sort(ii, l, i);
        		l = k;
        	}
        }
         
        int main() {
        	static int kk[N];
        	static char used[N];
        	int n, m, k, h, i, j;
         
        	scanf("%d%d%d", &n, &m, &k);
        	for (i = 0; i < n; i++)
        		eh[i] = (int *) malloc(2 * sizeof *eh[i]);
        	for (h = 0; h < n - 1; h++) {
        		scanf("%d%d", &i, &j), i--, j--;
        		ij[h] = i ^ j;
        		append(i, h), append(j, h);
        	}
        	dfs(-1, -1, 0, 0);
        	for (h = 0; h < cnt; h++) {
        		i = qu[h];
        		qq[i] = qq[i] ? qq[pp[i]] : i;
        	}
        	while (m--) {
        		static int ii[N];
         
        		scanf("%d", &cnt);
        		for (h = 0; h < cnt; h++)
        			scanf("%d", &ii[h]), ii[h]--;
        		sort(ii, 0, cnt);
        		for (h = 0; h < cnt; h++) {
        			i = ii[h], j = lca(ii[h], ii[(h - 1 + cnt) % cnt]);
        			kk[ta[i]]++, kk[ta[j]]--;
        		}
        	}
        	for (i = 1; i < n; i++)
        		kk[i] += kk[i - 1];
        	cnt = 0;
        	for (i = 0; i < n; i++)
        		if (kk[tb[i] - 1] - (ta[i] == 0 ? 0 : kk[ta[i] - 1]) >= k)
        			used[ff[i]] = 1, cnt++;
        	printf("%d\n", cnt);
        	for (h = 0; h < n - 1; h++)
        		if (used[h])
        			printf("%d ", h + 1);
        	printf("\n");
        	return 0;
        }

Compilation message (stderr)

railway.cpp: In function 'void append(int, int)':
railway.cpp:14:31: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   14 |          if (o >= 2 && (o & o - 1) == 0)
      |                             ~~^~~
railway.cpp: In function 'int main()':
railway.cpp:75:15: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   75 |          scanf("%d%d%d", &n, &m, &k);
      |          ~~~~~^~~~~~~~~~~~~~~~~~~~~~
railway.cpp:79:16: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   79 |           scanf("%d%d", &i, &j), i--, j--;
      |           ~~~~~^~~~~~~~~~~~~~~~
railway.cpp:91:16: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   91 |           scanf("%d", &cnt);
      |           ~~~~~^~~~~~~~~~~~
railway.cpp:93:17: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   93 |            scanf("%d", &ii[h]), ii[h]--;
      |            ~~~~~^~~~~~~~~~~~~~

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 16 / 16
• Subtask 6: 25 / 25