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// 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
}
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