#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 300000
#define INF 0x3f3f3f3f
int min(int a, int b) { return a < b ? a : b; }
int max(int a, int b) { return a > b ? a : b; }
int n, r, a, b;
int *ej[N], eo[N];
void append(int i, int j) {
int o = eo[i]++;
if (o >= 2 && (o & o - 1) == 0)
ej[i] = (int *) realloc(ej[i], o * 2 * sizeof *ej[i]);
ej[i][o] = j;
}
int ii[N], dd[N], pp[N], pp_[N], ll[N], ta[N], tb[N], qu[N];
void dfs1(int i) {
static int t_;
static int stack[N];
int o;
qu[ta[i] = t_++] = i;
stack[dd[i]] = i;
pp_[i] = dd[i] < a - 1 ? -1 : stack[dd[i] - a + 1];
ll[i] = 0;
for (o = eo[i]; o--; ) {
int j = ej[i][o];
if (j != pp[i]) {
dfs1(j);
ll[i] = max(ll[i], ll[j] + 1);
}
}
tb[i] = t_;
}
char dp[N], dq[N];
void mark(int l, int r, int d) {
int i, a;
for (a = l; a <= r; a++) {
i = qu[a];
if (dd[i] <= d && dq[i])
dq[i] = 0;
}
}
int solve(int k) {
static char dq_[N];
static int dd1[N], dd2[N];
int h, h_, i, j, j_, j1, j2, o, bad;
for (h = n - 1; h >= 0; h--) {
i = ii[h];
dd1[i] = i < k ? 0 : INF;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i])
dd1[i] = min(dd1[i], dd1[j] + 1);
}
}
memset(dq, 1, n * sizeof *dq), memset(dq_, 0, n * sizeof *dq_);
for (h = n - 1, h_ = n - 1; h >= 0; h--) {
i = ii[h];
while (h_ >= 0 && dd[j = ii[h_]] - dd[i] >= a) {
if (dq[j])
dq_[pp_[j]] = 1;
h_--;
}
if (ll[i] < a) {
if (dd1[i] > b)
dp[i] = 1;
else {
dp[i] = 0;
j_ = i >= k ? -1 : -2;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i] && dd1[j] < b)
j_ = j_ == -1 ? j : -2;
}
if (j_ == -2)
mark(ta[i], tb[i] - 1, dd[i] + b);
else if (j_ != -1)
mark(ta[i], ta[j_] - 1, dd[i] + b), mark(tb[j_], tb[i] - 1, dd[i] + b);
}
} else {
j_ = -1;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i] && dq_[j])
j_ = j_ == -1 ? j : -2;
}
if (j_ != -1)
dp[i] = 1;
else {
dp[i] = 0;
j_ = -2;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i] && ll[j] >= a - 1) {
j_ = j;
break;
}
}
if (j_ == -2)
mark(ta[i], tb[i] - 1, dd[i] + b);
else
mark(ta[i], ta[j_] - 1, dd[i] + b), mark(tb[j_], tb[i] - 1, dd[i] + b);
}
if (j_ != -2) {
bad = i < k;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i] && j != j_ && (ll[j] >= a - 1 || dd1[j] < b)) {
bad = 1;
break;
}
}
if (bad)
mark(ta[j_], tb[j_] - 1, dd[i] + b);
}
}
j1 = j2 = -1;
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != pp[i]) {
if (j1 == -1 || dd2[j1] > dd2[j])
j2 = j1, j1 = j;
else if (j2 == -1 || dd2[j2] > dd2[j])
j2 = j;
}
}
dd2[i] = !dp[i] ? 0 : (j1 == -1 || dd2[j1] == INF ? INF : dd2[j1] + 1);
for (o = eo[i]; o--; ) {
j = ej[i][o], j_ = j != j1 ? j1 : j2;
if (j_ != -1)
mark(ta[j], tb[j] - 1, dd[i] + b - (dd2[j_] + 1));
}
}
return dp[r];
}
int main() {
int cnt, h, i, j, o, k, lower, upper;
scanf("%d%d%d%d", &n, &r, &a, &b), r--;
if (a <= b) {
printf("1\n");
return 0;
}
for (i = 0; i < n; i++)
ej[i] = (int *) malloc(2 * sizeof *ej[i]);
for (h = 0; h < n - 1; h++) {
scanf("%d%d", &i, &j), i--, j--;
append(i, j), append(j, i);
}
cnt = 0;
dd[r] = 0, pp[r] = -1, ii[cnt++] = r;
for (h = 0; h < cnt; h++) {
i = ii[h];
for (o = 0; o < eo[i]; o++) {
j = ej[i][o];
if (j != pp[i])
dd[j] = dd[i] + 1, pp[j] = i, ii[cnt++] = j;
}
}
dfs1(r);
lower = 0, upper = n;
while (upper - lower > 1) {
k = (lower + upper) / 2;
if (solve(k))
lower = k;
else
upper = k;
}
printf("%d\n", upper);
return 0;
}
Compilation message
Main.c: In function 'append':
Main.c:17:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
17 | if (o >= 2 && (o & o - 1) == 0)
| ~~^~~
Main.c: In function 'main':
Main.c:154:2: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
154 | scanf("%d%d%d%d", &n, &r, &a, &b), r--;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Main.c:162:3: warning: ignoring return value of 'scanf' declared with attribute 'warn_unused_result' [-Wunused-result]
162 | scanf("%d%d", &i, &j), i--, j--;
| ^~~~~~~~~~~~~~~~~~~~~
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
348 KB |
Output is correct |
| 2 |
Correct |
0 ms |
348 KB |
Output is correct |
| 3 |
Correct |
0 ms |
348 KB |
Output is correct |
| 4 |
Correct |
0 ms |
348 KB |
Output is correct |
| 5 |
Correct |
0 ms |
348 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Execution timed out |
6067 ms |
54356 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
348 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
348 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
386 ms |
10320 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
348 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
348 KB |
Output is correct |
| 2 |
Correct |
0 ms |
348 KB |
Output is correct |
| 3 |
Correct |
0 ms |
348 KB |
Output is correct |
| 4 |
Correct |
0 ms |
348 KB |
Output is correct |
| 5 |
Correct |
0 ms |
348 KB |
Output is correct |
| 6 |
Execution timed out |
6067 ms |
54356 KB |
Time limit exceeded |
| 7 |
Halted |
0 ms |
0 KB |
- |
