LeetCode //C - 219. Contains Duplicate II

219. Contains Duplicate II

Given an integer array nums and an integer k , return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k .

Example 1:

Input: nums = [1,2,3,1], k = 3
Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1
Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2
Output: false

Constraints:

• 1 < = n u m s . l e n g t h < = 1 0 5 1 <= nums.length <= 10^5 1<=nums.length<=105
• − 1 0 9 < = n u m s [ i ] < = 1 0 9 -10^9 <= nums[i] <= 10^9 −109<=nums[i]<=109
• 0 < = k < = 1 0 5 0 <= k <= 10^5 0<=k<=105

From: LeetCode

Link: 219. Contains Duplicate II

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Solution:

Ideas：

1. Structure Definition: A structure Number is defined to store two integers: the value of an element from the nums array and its original index in the array.

2. Array Initialization: An array numbers of type Number is created and initialized with the values and corresponding indices from the input array nums.

3. Sorting: The numbers array is sorted by the values using the qsort function. The compare function is used to define the sorting order, which is based on the value field of the structure. After sorting, elements with the same value will be adjacent to each other, and their original indices can still be accessed.

4. Scanning for Duplicates: The sorted numbers array is then scanned to find adjacent pairs with the same value. If such a pair is found, the original indices are checked to see if the absolute difference between them is less than or equal to k. If this condition is met, the function returns true.

5. Memory Cleanup: The dynamically allocated memory for the numbers array is freed before exiting the function.

6. Result: If no such pair is found that meets the condition, the function returns false.

By sorting the numbers and keeping track of the original indices, this approach efficiently checks for duplicates within the specified range k. The sorting ensures that the same values are grouped together, making it easy to check the condition without needing a hash table.

Code:

typedef struct {
    int value;
    int index;
} Number;

int compare(const void *a, const void *b) {
    return ((Number*)a)->value - ((Number*)b)->value;
}

bool containsNearbyDuplicate(int* nums, int numsSize, int k) {
    if (k == 0 || numsSize <= 1) return false;
    
    Number* numbers = (Number*)malloc(numsSize * sizeof(Number));
    for (int i = 0; i < numsSize; i++) {
        numbers[i].value = nums[i];
        numbers[i].index = i;
    }
    
    qsort(numbers, numsSize, sizeof(Number), compare);
    
    for (int i = 0; i < numsSize - 1; i++) {
        if (numbers[i].value == numbers[i + 1].value && 
            abs(numbers[i].index - numbers[i + 1].index) <= k) {
            free(numbers);
            return true;
        }
    }
    
    free(numbers);
    return false;
}