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author | Jack Sangdahl <[email protected]> | 2024-10-10 20:36:22 -0600 |
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committer | Jack Sangdahl <[email protected]> | 2024-10-10 20:36:22 -0600 |
commit | 0c21b6ec40d59bedd0dccb8b6049f3b3fe7f344a (patch) | |
tree | d67a6bef5501ebf8fc6092e2e3f4e5351218187b /num_smallest_unoccupied_char.c | |
parent | 7187348d45fa427319707488e5affe5d5b97f708 (diff) | |
download | leetcode-0c21b6ec40d59bedd0dccb8b6049f3b3fe7f344a.tar.gz leetcode-0c21b6ec40d59bedd0dccb8b6049f3b3fe7f344a.zip |
1942. the number of the smallest unoccupied chair
Diffstat (limited to 'num_smallest_unoccupied_char.c')
-rw-r--r-- | num_smallest_unoccupied_char.c | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/num_smallest_unoccupied_char.c b/num_smallest_unoccupied_char.c new file mode 100644 index 0000000..b8babad --- /dev/null +++ b/num_smallest_unoccupied_char.c @@ -0,0 +1,96 @@ +// 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 +} |