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// 1942. The Number of the Smallest Unoccupied Chair
#include "leetcode.h"
/*
* there is a party where 'n' friends numbered from 0 to 'n - 1' are attending.
* there is an infinite number of chairs in this part that are numbered from 0
* to 'infinity'. when a friend arrives at the party, they sit on the unoccupied
* chair with the smallest number. when a friend leaves the party their chair
* becomes unoccupied at the moment they leave. if another friend arrives at
* that same moment, they can sit in that chair. you are given a 0-indexed 2d
* integer array 'times' where 'times[i] = [arrival[i], leaving[i]]' indicating
* the arrival and leaving times of the i'th friend respectively. and an integer
* 'targetFriend'. all arrival times are distinct. return the chair number that
* the friend numbered 'targetFriend' will sit on.
*/
int cmp(const void *a, const void *b) {
return (*(int **)a)[0] - (*(int **)b)[0];
}
void heap_down(int **chair, int *heap, int heap_size) {
int curr = 1, child = curr * 2;
while (child <= heap_size) {
if (child + 1 <= heap_size &&
chair[heap[child + 1]][0] < chair[heap[child]][0])
child++;
if (chair[heap[curr]][0] < chair[heap[child]][0])
break;
int tmp = heap[child];
heap[child] = heap[curr];
heap[curr] = tmp;
curr = child;
child *= 2;
}
}
void heap_up(int **chair, int *heap, int idx, int val) {
int curr = idx, parent = curr / 2;
while (parent >= 1) {
if (chair[heap[parent]][0] <= chair[val][0])
break;
heap[curr] = heap[parent];
curr = parent;
parent /= 2;
}
heap[curr] = val;
}
int smallestChair(int **times, int timesSize, int *timesColSize,
int targetFriend) {
int ans = 0, valid_idx = timesSize, invalid_idx = 0;
int **chair = (int **)malloc(timesSize * sizeof(int *));
int **qdata = (int **)malloc(timesSize * sizeof(int *));
int *valid = (int *)malloc((timesSize + 1) * sizeof(int));
int *invalid = (int *)malloc((timesSize + 1) * sizeof(int));
for (int i = 0; i < timesSize; i++) {
qdata[i] = (int *)malloc(3 * sizeof(int));
qdata[i][0] = times[i][0];
qdata[i][1] = times[i][1];
qdata[i][2] = i;
chair[i] = (int *)malloc(3 * sizeof(int));
chair[i][0] = chair[i][1] = i;
chair[i][2] = 0;
valid[i + 1] = i;
}
qsort(qdata, timesSize, sizeof(qdata[0]), cmp);
for (int i = 0; i < timesSize; i++) {
while (invalid_idx && chair[invalid[1]][0] <= qdata[i][0]) {
int target = invalid[i];
chair[target][0] = chair[target][1];
heap_up(chair, valid, ++valid_idx, target);
invalid[1] = invalid[invalid_idx--];
heap_down(chair, invalid, invalid_idx);
}
if (targetFriend == qdata[i][2])
ans = chair[valid[1]][1];
int target = valid[1];
chair[target][0] = chair[target][2] = qdata[i][1];
heap_up(chair, invalid, ++invalid_idx, target);
valid[1] = valid[valid_idx--];
heap_down(chair, valid, valid_idx);
}
for (int i = 0; i < timesSize; i++)
free(chair[i]), free(qdata[i]);
free(chair), free(qdata), free(valid), free(invalid);
return ans;
}
int main() {
int t1[3][2] = {{1, 4}, {2, 3}, {4, 6}}, t2[3][2] = {{3, 10}, {1, 5}, {2, 6}},
tcs1 = 2, tcs2 = 2;
printf("%d\n",
smallestChair((int **)t1, ARRAY_SIZE(t1), &tcs1, 1)); // expect: 1
printf("%d\n",
smallestChair((int **)t2, ARRAY_SIZE(t2), &tcs2, 0)); // expect: 2
}
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