Merge pull request neetcode-gh#1994 from seinlin/347

Add 0347-top-k-frequent-elements.c

c/0347-top-k-frequent-elements.c

@@ -0,0 +1,49 @@
+// A structure to represent an element of the heap.
+typedef struct {
+    int num;
+    int count;
+} Heap;
+
+static int compareHeap(const void* x, const void* y) {
+  return ((Heap*)y)->count - ((Heap*)x)->count;
+}
+
+/**
+ * Note: The returned array must be malloced, assume caller calls free().
+ */
+int* topKFrequent(int* nums, int numsSize, int k, int* returnSize){
+    int hash[20001] = {0};
+    Heap* heap;
+    int *res;
+    int i, j;
+    int c = 0;
+
+    for (i = 0; i < numsSize; i++) {
+        hash[nums[i]+10000]++;
+        if (hash[nums[i]+10000]) {
+            c++;
+        }
+    }
+
+    heap = (Heap*)malloc(sizeof(Heap) * c);
+    memset(heap, 0, sizeof(Heap) * c);
+
+    c = 0;
+    for (i = 0; i < 20001; i++) {
+        if(hash[i] > 0) {
+            heap[c].num = i - 10000;
+            heap[c].count = hash[i];
+            c++;
+        }
+    }
+    qsort(heap, c, sizeof(Heap), compareHeap);
+
+    c = 0;
+    res = (int*)malloc(sizeof(int) * k);
+    for (i = 0; i < k; i++) {
+        res[c++] = heap[i].num;
+    }
+
+    *returnSize = c; 
+    return res;
+}