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注：刘轩宇是抄的我的


struct group_info *groups_alloc(int gidsetsize){struct group_info *group_info;int nblocks;int i;nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;/* Make sure we always allocate at least one indirect block pointer */nblocks = nblocks ? : 1;group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);if (!group_info)return NULL;group_info->ngroups = gidsetsize;group_info->nblocks = nblocks;atomic_set(&group_info->usage, 1);if (gidsetsize <= NGROUPS_SMALL)group_info->blocks[0] = group_info->small_block;else {for (i = 0; i < nblocks; i++) {gid_t *b;b = (void *)__get_free_page(GFP_USER);if (!b)goto out_undo_partial_alloc;group_info->blocks[i] = b;}}return group_info;out_undo_partial_alloc:while (--i >= 0) {free_page((unsigned long)group_info->blocks[i]);}kfree(group_info);return NULL;}EXPORT_SYMBOL(groups_alloc);void groups_free(struct group_info *group_info){if (group_info->blocks[0] != group_info->small_block) {int i;for (i = 0; i < group_info->nblocks; i++)free_page((unsigned long)group_info->blocks[i]);}kfree(group_info);}EXPORT_SYMBOL(groups_free);/* export the group_info to a user-space array */static int groups_to_user(gid_t __user *grouplist,const struct group_info *group_info){int i;unsigned int count = group_info->ngroups;for (i = 0; i < group_info->nblocks; i++) {unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);unsigned int len = cp_count * sizeof(*grouplist);if (copy_to_user(grouplist, group_info->blocks[i], len))return -EFAULT;grouplist += NGROUPS_PER_BLOCK;count -= cp_count;}return 0;}/* fill a group_info from a user-space array - it must be allocated already */static int groups_from_user(struct group_info *group_info,gid_t __user *grouplist){int i;unsigned int count = group_info->ngroups;for (i = 0; i < group_info->nblocks; i++) {unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);unsigned int len = cp_count * sizeof(*grouplist);if (copy_from_user(group_info->blocks[i], grouplist, len))return -EFAULT;grouplist += NGROUPS_PER_BLOCK;count -= cp_count;}return 0;}/* a simple Shell sort */static void groups_sort(struct group_info *group_info){int base, max, stride;int gidsetsize = group_info->ngroups;for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1); /* nothing */stride /= 3;while (stride) {max = gidsetsize - stride;for (base = 0; base < max; base++) {int left = base;int right = left + stride;gid_t tmp = GROUP_AT(group_info, right);while (left >= 0 && GROUP_AT(group_info, left) > tmp) {GROUP_AT(group_info, right) =GROUP_AT(group_info, left);right = left;left -= stride;}GROUP_AT(group_info, right) = tmp;}stride /= 3;}}/* a simple bsearch */int groups_search(const struct group_info *group_info, gid_t grp){unsigned int left, right;if (!group_info)return 0;left = 0;right = group_info->ngroups;while (left < right) {unsigned int mid = left + (right - left)/2;if (grp > GROUP_AT(group_info, mid))left = mid + 1;else if (grp < GROUP_AT(group_info, mid))right = mid;elsereturn 1;}return 0;}/*** set_groups - Change a group subscription in a set of credentials* @new: The newly prepared set of credentials to alter* @group_info: The group list to install** Validate a group subscription and, if valid, insert it into a set* of credentials.*/int set_groups(struct cred *new, struct group_info *group_info){put_group_info(new->group_info);groups_sort(group_info);get_group_info(group_info);new->group_info = group_info;return 0;}EXPORT_SYMBOL(set_groups);/*** set_current_groups - Change current's group subscription* @group_info: The group list to impose** Validate a group subscription and, if valid, impose it upon current's task* security record.*/int set_current_groups(struct group_info *group_info){struct cred *new;int ret;new = prepare_creds();if (!new)return -ENOMEM;ret = set_groups(new, group_info);if (ret < 0) {abort_creds(new);return ret;}return commit_creds(new);}EXPORT_SYMBOL(set_current_groups);SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist){const struct cred *cred = current_cred();int i;if (gidsetsize < 0)return -EINVAL;/* no need to grab task_lock here; it cannot change */i = cred->group_info->ngroups;if (gidsetsize) {if (i > gidsetsize) {i = -EINVAL;goto out;}if (groups_to_user(grouplist, cred->group_info)) {i = -EFAULT;goto out;}}out:return i;}/**   SMP: Our groups are copy-on-write. We can set them safely*  without another task interfering.*/SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist){struct group_info *group_info;int retval;if (!nsown_capable(CAP_SETGID))return -EPERM;if ((unsigned)gidsetsize > NGROUPS_MAX)return -EINVAL;group_info = groups_alloc(gidsetsize);if (!group_info)return -ENOMEM;retval = groups_from_user(group_info, grouplist);if (retval) {put_group_info(group_info);return retval;}retval = set_current_groups(group_info);put_group_info(group_info);return retval;}/** Check whether we're fsgid/egid or in the supplemental group..*/int in_group_p(gid_t grp){const struct cred *cred = current_cred();int retval = 1;if (grp != cred->fsgid)retval = groups_search(cred->group_info, grp);return retval;}EXPORT_SYMBOL(in_group_p);int in_egroup_p(gid_t grp){const struct cred *cred = current_cred();int retval = 1;if (grp != cred->egid)retval = groups_search(cred->group_info, grp);return retval;}
|#include<bits/stdc++.h>
using namespace std;const int N = 100010, M = 400010;int n, m;
int h[N], e[M],w[M], ne[M], idx;
int dist[N];
int q[N];
void add(int a, int b, int c){e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++;
}
// 求1号点到n号点的最短路：边权为1
// 返回值为最短路，含义是：从1号点到n号点使用的边权小于等于mid 的条数
//如果 返回值 == 6，说明从1号点到n号点，使用边权小于等于mid的边的条数为6条
int bfs(int mid){memset(dist, 0x3f, sizeof dist);dist[1] = 0;int hh = 0, tt = 0;q[0] = 1;while( hh <= tt){int t = q[hh ++];for(int i = h[t]; ~i; i = ne[i]){if(w[i] > mid)  continue;int j = e[i];if(dist[j] > dist[t] + 1){dist[j] = dist[t] + 1;q[++tt] = j;}}}return dist[n];
}int main(){cin >> n >> m;memset(h, -1, sizeof h);while(m --){int a, b, c;cin >> a >> b >> c;add(a, b, c), add(b, a, c);}// 二分，枚举合适的最优边权int l = 0, r = 1e6;while(l < r){int mid = l + r >> 1;if(bfs(mid) <= n) r = mid;else l = mid + 1;}//输出二分出来的分界点，二分退出时l == rcout << r << endl;
}

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