Create 0347-Top-K-Frequent-Elements.c

Create the C solution as the same solution in the YouTube video "https://www.youtube.com/watch?v=YPTqKIgVk-k"

Author: MHamiid

c/0347-Top-K-Frequent-Elements.c

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+#define ALLOCATION_SIZE 100  // Allocation size of the numsArrLen in frequencyArrItem
+
+typedef struct hash_entry {
+    int num;            /* we'll use this field as the key */
+    int count;
+    UT_hash_handle hh; /* makes this structure hashable */
+}hash_entry;
+
+typedef struct frequencyArrItem
+{
+    int* numsArr;
+    int numsArrLen;
+    int index;  // Points to the first empty space in numsArr
+}frequencyArrItem;
+
+/**
+ * Note: The returned array must be malloced, assume caller calls free().
+ */
+int* topKFrequent(int* nums, int numsSize, int k, int* returnSize){
+    int* result = (int*)malloc(k * sizeof(int));
+    *returnSize = k;
+    int resultIndex = 0; // Points to the first empty space in result
+    hash_entry* NumFreqMap = NULL;
+    frequencyArrItem frequencyArr[numsSize + 1]; // Index is the count/frequency and the element is an array of numbers with this frequency
+    memset(frequencyArr, 0, (numsSize + 1) * sizeof(frequencyArrItem)); // Initialize with NULL and zeros
+
+    for(int i = 0; i < numsSize; i++)
+    {
+        hash_entry* retrievedMapEntry;
+        HASH_FIND_INT(NumFreqMap, &nums[i], retrievedMapEntry);
+
+        // If the number already exists in the map then increment its count
+        if(retrievedMapEntry)
+        {
+            retrievedMapEntry->count += 1;
+        }
+        else
+        {
+            // If the number doesn't exist in the map then create a new map entry for it and add it to the map
+            hash_entry* mapEntryToAdd = (hash_entry*)malloc(sizeof(hash_entry)); 
+            mapEntryToAdd->num = nums[i];
+            mapEntryToAdd->count = 1; 
+            HASH_ADD_INT(NumFreqMap, num, mapEntryToAdd);
+        }
+    }
+    
+    // Loop over all the entries in the hash map
+    for (hash_entry* mapEntry = NumFreqMap; mapEntry != NULL; mapEntry = mapEntry->hh.next) {
+        frequencyArrItem* freq = frequencyArr + mapEntry->count;
+
+        // If the nums list for this frequency has not been created yet
+        if(freq->numsArrLen == 0)
+        {
+            freq->numsArrLen = ALLOCATION_SIZE;
+            freq->numsArr = (int*)malloc(freq->numsArrLen * sizeof(int));
+        }
+        // If the nums list exceeded the current allocated size, then reallocate
+        else if(freq->index == freq->numsArrLen)
+        {
+            freq->numsArrLen += ALLOCATION_SIZE;
+            freq->numsArr = (int*)realloc(freq->numsArr, freq->numsArrLen * sizeof(int));
+        }
+
+        freq->numsArr[freq->index++] = mapEntry->num; 
+    }
+
+    // Loop over the frequencies starting from the highest frequency
+    for(int i = numsSize; i >= 1; i--) // Note that we are looping until i == 1, as at index 0 it is just empty
+    {
+        frequencyArrItem* freq = frequencyArr + i;
+        // If there is nums that exist at this particular frequency
+        for(int j = 0; j < freq->index; j++)
+        {
+            // If we have added all the elements we need to the result
+            if(k-- == 0)
+            {
+                return result;
+            }
+
+            // Add the num to the result then increment the index
+            result[resultIndex++] = freq->numsArr[j];
+        }
+    }
+
+    return result;
+}