"Contains Duplicate II"

Author: lennylxx

README.md

@@ -31,7 +31,7 @@ You can build all the files using `make` (Use MinGW GCC and GNU Make on Windows)
 | 222 | [Count Complete Tree Nodes]                                  | [C](src/222.c)     |
 | 221 | [Maximal Square]                                             |                    |
 | 220 | [Contains Duplicate III]                                     |                    |
-| 219 | [Contains Duplicate II]                                      |                    |
+| 219 | [Contains Duplicate II]                                      | [C](src/219.c)     |
 | 218 | [The Skyline Problem]                                        |                    |
 | 217 | [Contains Duplicate]                                         | [C](src/217.c)     |
 | 216 | [Combination Sum III]                                        |                    |

src/219.c

@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct HashNode {
+    int data;
+    int index;
+    struct HashNode *next;
+};
+
+static inline int hash(int num, int size) {
+    int index = num % size;
+    return (index > 0) ? (index) : (-index);
+}
+
+bool containsNearbyDuplicate(int* nums, int numsSize, int k) {
+    if (numsSize < 2) return false;
+    bool duplicated = false;
+
+    int hash_size = numsSize / 2 + 1; /* proper size can be faster */
+    struct HashNode **hash_table
+        = (struct HashNode **)calloc(hash_size, sizeof(struct HashNode *));
+
+    int i;
+    for (i = 0; i < numsSize; i++) {
+        int index = hash(nums[i], hash_size);
+        struct HashNode **p = hash_table + index;
+
+        while (*p) {
+            if ((*p)->data == nums[i]) {
+                int distance = abs((*p)->index - i);
+                if (distance <= k) {
+                    duplicated = true;
+                    goto OUT;
+                }
+                else {
+                    (*p)->index = i; /* update to nearer index */
+                }
+            }
+            p = &((*p)->next);
+        }
+
+        struct HashNode *new_node
+            = (struct HashNode *)malloc(sizeof(struct HashNode));
+        new_node->data = nums[i];
+        new_node->index = i;
+        new_node->next = NULL;
+
+        *p = new_node;
+    }
+
+OUT:
+    for (i = 0; i < hash_size; i++) {
+        struct HashNode *t = hash_table[i];
+        struct HashNode *x = NULL;
+        while (t) {
+            x = t->next;
+            free(t);
+            t = x;
+        }
+    }
+    free(hash_table);
+
+    return duplicated;
+}
+
+int main() {
+    int nums[] = { 1, 3, 5, 7, 9, 2, 7, 4, 7 };
+    /* should be true */
+    printf("%d\n", containsNearbyDuplicate(nums, sizeof(nums) / sizeof(nums[0]), 2));
+
+    /* should be false */
+    printf("%d\n", containsNearbyDuplicate(nums, sizeof(nums) / sizeof(nums[0]), 1));
+
+    return 0;
+}