Adding MergeSort 3way in C

Sorting Algorithm/mergesort_3way.c

@@ -0,0 +1,119 @@
+/*
+    Code made by Pedro Perez
+    GitHub: https://github.com/pedrousp
+
+    This code works in the following steps:
+    1. Reads an integer from stdin and stores it in size_array variable
+    2. Allocates size_array * 4 bytes in heap memory for the array
+    3. Reads size_array integers from stdin an stores it in each address of the array
+    4. Calls mergesort_3way, which is a recursive function. It'll split the array in three pieces and order it
+    5. Frees the memory allocated for the array
+
+*/
+
+
+
+#include<stdlib.h>
+#include<stdio.h>
+
+int input_integer();
+int *create_array(int);
+void mergesort_3way(int*, int, int);
+void merge(int*, int, int, int, int);
+
+int main(int argc, char **argv){
+    int size_array = input_integer();
+    int *array = create_array(size_array);
+    mergesort_3way(array, 0, size_array-1);
+    free(array);
+    return 0;
+}
+
+int input_integer(){
+    int integer;
+    scanf("%d", &integer);
+    return integer;
+}
+
+int *create_array(int size){
+    int *array = malloc(size * sizeof(int));
+    for(int i = 0; i < size; i++){
+        array[i] = input_integer();
+    }
+    return array;
+}
+
+void mergesort_3way(int *array, int begin, int end){
+    //Base -> returns if it cannot split in lowest pieces
+    if(end <= begin)
+        return;
+
+    int difference = end - begin;
+
+    //Defines the split range
+    int split1 = begin + (difference / 3);
+    int split2 = begin + (2 * (difference / 3)) + 1;
+
+    //Calls a recursive function setting a new range to split the array
+    mergesort_3way(array, begin, split1);
+    mergesort_3way(array, split1+1, split2);
+    mergesort_3way(array, split2+1, end);
+
+    //After the recursive functions return, then it'll merge the values to order them
+    merge(array, begin, split1, split2, end);
+}
+
+void merge(int *array, int begin, int split1, int split2, int end){
+    //Creates an auxiliar array to help storing the values
+    int *auxiliar_array = malloc((end - begin + 1) * sizeof(int));
+    int i = begin, j = split1 + 1, k = split2 + 1, l = 0;
+
+    //From the three pieces, stores the lowest numbers
+    while(i <= split1 && j <= split2 && k <= end){
+        if(array[i] <= array[j] && array[i] <= array[k])
+            auxiliar_array[l++] = array[i++];
+        else if(array[j] <= array[i] && array[j] <= array[k])
+            auxiliar_array[l++] = array[j++];
+        else
+            auxiliar_array[l++] = array[k++];
+    }
+
+    //From the two remaining pieces, stores the lowest numbers
+    while(i <= split1 && j <= split2){
+        if(array[i] <= array[j])
+            auxiliar_array[l++] = array[i++];
+        else
+            auxiliar_array[l++] = array[j++];
+    }
+
+    while(j <= split2 && k <= end){
+        if(array[j] <= array[k])
+            auxiliar_array[l++] = array[j++];
+        else
+            auxiliar_array[l++] = array[k++];
+    }
+
+    while(i <= split1 && k <= end){
+        if(array[i] <= array[k])
+            auxiliar_array[l++] = array[i++];
+        else
+            auxiliar_array[l++] = array[k++];
+    }
+
+    //Finish storing the remaining values
+    while(i <= split1)
+        auxiliar_array[l++] = array[i++];
+
+    while(j <= split2)
+        auxiliar_array[l++] = array[j++];
+
+    while(k <= end)
+        auxiliar_array[l++] = array[k++];
+
+    //Copies the values back to the original array
+    for(int i = begin, k = 0; i <= end; i++, k++)
+        array[i] = auxiliar_array[k];
+
+    //Frees the memory allocated to the auxiliar array
+    free(auxiliar_array);
+}