diff options
Diffstat (limited to 'max_employees_invited.c')
-rw-r--r-- | max_employees_invited.c | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/max_employees_invited.c b/max_employees_invited.c new file mode 100644 index 0000000..1537ae4 --- /dev/null +++ b/max_employees_invited.c @@ -0,0 +1,78 @@ +// 2127. Maximum Employees to Be Invited to a Meeting +#include "leetcode.h" + +/* + * a company is organising a meeting and has a list of 'n' employees, waiting to + * be invited. they have arrange for a large circular table, capable of seating + * any number of employees. the employees are numbered from 0 to 'n - 1'. each + * employee has a favourite person and they will attend the meeting only if they + * can sit next to their favourite person. the favourite person of an employee + * is not themselves. given a 0 indexed integer array 'favorite' where + * 'favorite[i]' denotes the favourite person of the i'th employee, return the + * maximum number of employees that can be invited. + */ + +void topo_sort(const int *favorite, int *indegrees, int *chain_lens, int *stack, + int node_cnt) { + int stack_idx = 0; + for (int i = 0; i < node_cnt; i++) + if (!indegrees[i]) + stack[stack_idx++] = i; + while (stack_idx) { + int node = stack[--stack_idx], nn = chain_lens[node], + parent = favorite[node], pn = chain_lens[parent]; + if (pn <= nn) + chain_lens[parent] = nn + 1; + indegrees[parent]--; + if (!indegrees[parent]) + stack[stack_idx++] = parent; + } +} + +int traverse(const int *favorite, int *unvis, const int *chain_lens, + int node_cnt) { + int largest = 0, sum = 0; + for (int i = 0; i < node_cnt; i++) { + if (!unvis[i]) + continue; + int start = i, curr = i, cn = 0; + do { + unvis[curr] = 0; + cn++; + curr = favorite[curr]; + } while (curr != start); + if (cn > 2) + largest = fmax(largest, cn); + else + sum += chain_lens[curr] + chain_lens[favorite[curr]] + 2; + } + return fmax(largest, sum); +} + +int dfs(int *favorite, int favoriteSize) { + int *buf = (int *)malloc(3 * favoriteSize * sizeof(int)); + int *indegrees = buf; + memset(indegrees, 0, favoriteSize * sizeof(int)); + int *chain_lens = indegrees + favoriteSize; + memset(chain_lens, 0, favoriteSize * sizeof(int)); + int *stack = chain_lens + favoriteSize; + for (int i = 0; i < favoriteSize; i++) { + int parent = favorite[i]; + indegrees[parent]++; + } + topo_sort(favorite, indegrees, chain_lens, stack, favoriteSize); + int ans = traverse(favorite, indegrees, chain_lens, favoriteSize); + free(buf); + return ans; +} + +int maximumInvitations(int *favorite, int favoriteSize) { + return dfs(&favorite[0], favoriteSize); +} + +int main() { + int f1[] = {2, 2, 1, 2}, f2[] = {1, 2, 0}, f3[] = {3, 0, 1, 4, 1}; + printf("%d\n", maximumInvitations(f1, ARRAY_SIZE(f1))); // expect: 3 + printf("%d\n", maximumInvitations(f2, ARRAY_SIZE(f2))); // expect: 3 + printf("%d\n", maximumInvitations(f3, ARRAY_SIZE(f3))); // expect: 4 +} |