// 778. Swim in Rising Water #include "leetcode.h" /* * you are given an 'n x n' integer matrix 'grid' where each value 'grid[i][j]' * represnts the elevation at that point '(i, j)'. it starts raining and water * gradually rises over time. at time 't', the water level is 't', meaning any * cell with elevation less than or equal to 't' is submerged or reachable. you * can swim from a square to another 4-direction adjacent square if and only if * the elevation of both squares individually are at most 't'. you can swim * infinite distances in zero time. of course, you must stay within the * boundaries of the grid. return the minimum time until you can reach the * bottom right . you can swim infinite distances in zero time. of course, you * must stay within the boundaries of the grid. return the minimum time until * you can reach the bottom right square if you start at the top left. you can * swim infinite distances in zero time. of course, you must stay within the * boundaries of the grid. return the minimum time until you can reach the * bottom right square if you start at the top left..square if you start at the * top left. */ static int dir[4][2] = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}}; struct node { int val; int row; int col; }; struct pq { int size; int capacity; struct node *data; }; void swap(struct node *a, struct node *b) { struct node tmp = *a; *a = *b; *b = tmp; } struct pq *pq_init(int capacity) { struct pq *obj = (struct pq *)malloc(sizeof(struct pq)); obj->size = 0; obj->capacity = capacity; obj->data = (struct node *)malloc(capacity * sizeof(struct node)); return obj; } void pq_free(struct pq *obj) { free(obj->data); free(obj); } void min_heapify(struct pq *obj, int idx) { int smallest = idx, left = idx * 2 + 1, right = idx * 2 + 2; if (left < obj->size && obj->data[left].val < obj->data[smallest].val) smallest = left; if (right < obj->size && obj->data[right].val < obj->data[smallest].val) smallest = right; if (smallest != idx) { swap(&obj->data[idx], &obj->data[smallest]); min_heapify(obj, smallest); } } void push(struct pq *obj, int val, int row, int col) { int idx = obj->size; struct node n = {val, row, col}; obj->data[(obj->size)++] = n; while (idx && obj->data[(idx - 1) / 2].val > obj->data[idx].val) { swap(&obj->data[(idx - 1) / 2], &obj->data[idx]); idx = (idx - 1) / 2; } } struct node pop(struct pq *obj) { struct node root = obj->data[0]; obj->data[0] = obj->data[--(obj->size)]; min_heapify(obj, 0); return root; } bool is_empty(struct pq *obj) { return !obj->size; } int swimInWater(int **grid, int gridSize, int *gridColSize) { int total = gridSize * (*gridColSize); struct pq *heap = pq_init(total); push(heap, grid[0][0], 0, 0); grid[0][0] = -1; while (!is_empty(heap)) { struct node tmp = pop(heap); for (int i = 0; i < 4; i++) { int x = tmp.row + dir[i][0]; int y = tmp.col + dir[i][1]; if (x >= 0 && x < gridSize && y >= 0 && y < *gridColSize && grid[x][y] != -1) { int max = grid[x][y] > tmp.val ? grid[x][y] : tmp.val; if (x == gridSize - 1 && y == (*gridColSize) - 1) { pq_free(heap); return max; } push(heap, max, x, y); grid[x][y] = -1; } } } pq_free(heap); return 0; } int main() { int g1i[2][2] = {{0, 2}, {1, 3}}, g2i[5][5] = {{0, 1, 2, 3, 4}, {24, 23, 22, 21, 5}, {12, 13, 14, 15, 16}, {11, 17, 18, 19, 20}, {10, 9, 8, 7, 6}}; struct two_d_arr *g1 = two_d_arr_init(ARRAY_SIZE(g1i), ARRAY_SIZE(g1i[0]), g1i); struct two_d_arr *g2 = two_d_arr_init(ARRAY_SIZE(g2i), ARRAY_SIZE(g2i[0]), g2i); printf("%d\n", swimInWater(g1->arr, g1->row_size, g1->col_size)); // expect: 3 printf("%d\n", swimInWater(g2->arr, g2->row_size, g2->col_size)); // expect: // 16 two_d_arr_free(g1); two_d_arr_free(g2); }