// 1964. Find the Longest Valid Obstacle Course at Each Position #include "leetcode.h" /* * you want to build obstacle courses. you are given a 0-indexed integer array * 'obstacles' of length 'n' where 'obstacles[i]' describes the height of the * i'th obstacle. for every index 'i' between 0 and 'n - 1' (inclusive), find * the length of the longest obstacle course in 'obstacles' such that: * - you choose any number of obstacles between 0 and 'i' inclusive * - you must include the i'th obstacle in the course * - you must put the chosen obstacles in the same order as they appear in * 'obstacles' * - every obstacle (except the first) is taller than or the same height as the * obstacle immediately before it return an array 'ans' of length 'n', where * 'ans[i]' is the length of the longest obstacle course for index 'i' as * described above */ int find(int *arr, int start, int end, int target) { while (start < end) { int mid = start + (end - start) / 2; if (arr[mid] == target) start = mid + 1; else if (arr[mid] > target) end = mid; else start = mid + 1; } return start; } int *longestObstacleCourseAtEachPosition(int *obstacles, int obstaclesSize, int *returnSize) { int *ans = (int *)calloc(obstaclesSize, sizeof(int)); int *cnt = (int *)calloc(obstaclesSize, sizeof(int)), n = 1; ans[0] = 1; cnt[0] = obstacles[0]; for (int i = 1; i < obstaclesSize; i++) { int idx = find(cnt, 0, n, obstacles[i]); if (idx == n) cnt[n++] = obstacles[i]; else cnt[idx] = obstacles[i]; ans[i] = idx + 1; } *returnSize = obstaclesSize; free(cnt); return ans; } int main() { int o1[] = {1, 2, 3, 2}, o2[] = {2, 2, 1}, o3[] = {3, 1, 5, 6, 4, 2}, rs1, rs2, rs3; int *locaep1 = longestObstacleCourseAtEachPosition(o1, ARRAY_SIZE(o1), &rs1); int *locaep2 = longestObstacleCourseAtEachPosition(o2, ARRAY_SIZE(o2), &rs2); int *locaep3 = longestObstacleCourseAtEachPosition(o3, ARRAY_SIZE(o3), &rs3); for (int i = 0; i < rs1; i++) printf("%d ", locaep1[i]); // expect: 1 2 3 3 printf("\n"); for (int i = 0; i < rs2; i++) printf("%d ", locaep2[i]); // expect: 1 2 1 printf("\n"); for (int i = 0; i < rs3; i++) printf("%d ", locaep3[i]); // expect: 1 1 2 3 2 2 printf("\n"); free(locaep1), free(locaep2), free(locaep3); }