aboutsummaryrefslogtreecommitdiff
path: root/reconstruct_itinerary.c
blob: a625ecea415bd6ada551de10c47169a28dcbdd8f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
// 332. Reconstruct Itinerary
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * given a list of airline 'tickets' where 'tickets[i] = [from[i], to[i]]'
 * represents the departure and the arrival airpots of one flight. reconstruct
 * the itinerary in order and return it. all of the tickets belong to a man who
 * departs from "JFK", thus, the itinerary must begin with "JFK". if there are
 * multiple valid entires, you should return the itinerary that has the smallest
 * lexical order when read as a string. you may assume all tickets form at least
 * one valid itinerary. you must all the tickets once and only once.
 */

#define MAGIC_NUM 31L
#define MODULE_NUM 1000007L
#define NEXT_MAX 50
long mod(long n, long m) { return (n % m + m) % m; }

long hash(char *charater) {
  long hash_value = 0;
  hash_value += MAGIC_NUM * charater[0];
  hash_value = mod(hash_value, MODULE_NUM);

  hash_value += MAGIC_NUM * MAGIC_NUM * charater[1];
  hash_value = mod(hash_value, MODULE_NUM);

  hash_value += MAGIC_NUM * MAGIC_NUM * MAGIC_NUM * charater[2];
  hash_value = mod(hash_value, MODULE_NUM);

  return hash_value;
}

typedef struct _node_t {
  struct _node_t *adj_list[NEXT_MAX];
  int adj_count;
  int i_count;
  struct _node_t *left;
  struct _node_t *right;
  long hash_val;
  char *string_p;
} node_t;

node_t *generate_itinerary(long hash_val) {
  node_t *node = malloc(sizeof(node_t));
  for (int i = 0; i < NEXT_MAX; i++)
    node->adj_list[i] = NULL;
  node->hash_val = hash_val;
  node->adj_count = 0;
  node->i_count = 0;
  node->left = NULL;
  node->right = NULL;

  return node;
}

node_t *insert_bst(node_t *node, long hash_val, node_t **insert_node) {
  if (node == NULL) {
    node = generate_itinerary(hash_val);
    *insert_node = node;
    return node;
  }

  if (node->hash_val == hash_val) {
    return NULL;
  } else if (hash_val < node->hash_val) {
    node_t *temp = insert_bst(node->left, hash_val, insert_node);
    if (temp != node->left) {
      node->left = temp;
      *insert_node = temp;
    }
  } else if (hash_val > node->hash_val) {
    node_t *temp = insert_bst(node->right, hash_val, insert_node);
    if (temp != node->right) {
      node->right = temp;
      *insert_node = temp;
    }
  }

  return node;
}

node_t *search_in_bst(node_t *node, long hash_val) {
  if (node == NULL)
    return NULL;

  if (hash_val == node->hash_val) {
    return node;
  }
  if (hash_val < node->hash_val) {
    return search_in_bst(node->left, hash_val);
  } else if (hash_val > node->hash_val) {
    return search_in_bst(node->right, hash_val);
  } else {
    return NULL;
  }
}

int laxical_determine(char *s1, char *s2) {
  for (int i = 0; i < 3; i++) {
    if (s1[i] < s2[i]) {
      return 0;
    } else if (s1[i] > s2[i]) {
      return 1;
    }
  }

  return 0;
}

void swap_node(node_t **n1, node_t **n2) {
  node_t *temp = *n1;
  *n1 = *n2;
  *n2 = temp;
}

void print_bst(node_t *node) {
  if (node == NULL)
    return;

  print_bst(node->left);
  printf("[%s] hash: %ld, count: %d\n", node->string_p, node->hash_val,
         node->adj_count);
  print_bst(node->right);
}

void traverse_graph(node_t *node, char ***result, int *count) {
  while (node->i_count < node->adj_count) {
    traverse_graph(node->adj_list[node->i_count++], result, count);
  }
  // post-order
  // printf("traverse: %s\n", node->string_p);
  memcpy((*result)[*count], node->string_p, 3 * sizeof(char));
  (*count)++;
}

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
char **findItinerary(char ***tickets, int ticketsSize, int *ticketsColSize,
                     int *returnSize) {
  char **result = malloc(ticketsSize * 2 * sizeof(char *));
  long start_hash = hash("JFK");
  // printf("start hash: %ld\n", start_hash);

  for (int i = 0; i < ticketsSize * 2; i++) {
    result[i] = malloc(4 * sizeof(char));
    memset(result[i], 0, 4 * sizeof(char));
  }

  node_t *st_itinerary = NULL;
  node_t *bst_root = NULL;
  int node_count = 0;

  for (int i = 0; i < ticketsSize; i++) {
    long from_hash = hash(tickets[i][0]);
    long to_hash = hash(tickets[i][1]);

    node_t *from_node = search_in_bst(bst_root, from_hash);
    node_t *to_node = search_in_bst(bst_root, to_hash);

    if (NULL == from_node) {
      bst_root = insert_bst(bst_root, from_hash, &from_node);
      node_count++;
    }
    if (NULL == to_node) {
      bst_root = insert_bst(bst_root, to_hash, &to_node);
      node_count++;
    }

    from_node->string_p = tickets[i][0];
    to_node->string_p = tickets[i][1];

    if (from_hash == start_hash)
      st_itinerary = from_node;

    from_node->adj_list[from_node->adj_count++] = to_node;
    for (int k = from_node->adj_count - 2; k >= 0; k--) {
      if (laxical_determine(from_node->adj_list[k]->string_p,
                            from_node->adj_list[k + 1]->string_p)) {
        swap_node(&from_node->adj_list[k], &from_node->adj_list[k + 1]);
      }
    }
  }

  if (st_itinerary == NULL)
    return NULL;
  int col = 0;
  traverse_graph(st_itinerary, &result, &col);

  for (int i = 0; i < col >> 1; i++) {
    char *temp = result[i];
    result[i] = result[col - i - 1];
    result[col - i - 1] = temp;
  }

  *ticketsColSize = col;
  *returnSize = col;

  return result;
}