mirror of https://github.com/TheAlgorithms/C
69 lines
2.3 KiB
C
69 lines
2.3 KiB
C
/**
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* @file
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* @brief Implementation of [Floyd's Cycle
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* Detection](https://en.wikipedia.org/wiki/Cycle_detection) algorithm
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* @details
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* Given an array of integers containing `n + 1` integers, where each
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* integer is in the range [1, n] inclusive. If there is only one duplicate
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* number in the input array, this algorithm returns the duplicate number in
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* O(1) space and the time complexity is less than O(n^2) without modifying the
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* original array, otherwise, it returns -1.
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* @author [Swastika Gupta](https://github.com/Swastyy)
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*/
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#include <assert.h> /// for assert
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#include <inttypes.h> /// for uint32_t
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#include <stdio.h> /// for IO operations
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/**
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* @brief The main function implements the search algorithm
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* @tparam T type of array
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* @param in_arr the input array
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* @param n size of the array
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* @returns the duplicate number
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*/
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uint32_t duplicateNumber(const uint32_t *in_arr, size_t n)
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{
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if (n <= 1) { // to find duplicate in an array its size should be at least 2
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return -1;
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}
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uint32_t tortoise = in_arr[0]; ///< variable tortoise is used for the longer
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///< jumps in the array
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uint32_t hare = in_arr[0]; ///< variable hare is used for shorter jumps in the array
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do { // loop to enter the cycle
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tortoise = in_arr[tortoise]; // tortoise is moving by one step
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hare = in_arr[in_arr[hare]]; // hare is moving by two steps
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} while (tortoise != hare);
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tortoise = in_arr[0];
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while (tortoise != hare) { // loop to find the entry point of cycle
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tortoise = in_arr[tortoise];
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hare = in_arr[hare];
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}
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return tortoise;
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}
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/**
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* @brief Self-test implementations
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* @returns void
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*/
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static void test()
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{
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uint32_t arr[] = {1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610}; // input array
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size_t n = sizeof(arr) / sizeof(int);
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printf("1st test... ");
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uint32_t index = duplicateNumber(arr, n); // calling the duplicateNumber function to check which number occurs twice in the array
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assert(index == 1); // the number which occurs twice is 1 or not
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printf("passed\n");
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}
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/**
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* @brief Main function
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* @returns 0 on exit
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*/
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int main()
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{
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test(); // run self-test implementations
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return 0;
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}
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