以下代码对单词数组进行排序,处理小数组,并对大数组进行分段(> 400000 个单词,尽管我没有找到限制)。它被一个程序调用,该程序将一个单词数组(从文件中读取)传递给它以进行排序并测试其是否成功:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "csort.h"
#include "sort.h"
// array points to array of pointers to strings, count is number of entries in array
void sortC(char** array, unsigned int count){
array = merge_sort(array, count);
// testing:
/*for (int i = 0; i < count; i++){
printf("%s ", array[i]);
}*/
}
char** merge_sort(char** array, int count){
if (count <= 1) return array;
else {
int lcount = 0;
int rcount = 0;
int middle = count/2;
lcount = middle;
char* left[lcount];
subArray(array, left, 0, middle);
rcount = count-middle;
char* right[rcount];
subArray(array, right, middle, count);
return merge(merge_sort(left, lcount), merge_sort(right, rcount), array, 0, lcount, rcount);
}
}
void subArray(char** array, char** subarray, int start, int end){
int ai; // index in original array
int si; // index in subarray
for (ai = start, si = 0; ai < end; ai++, si++){
subarray[si] = array[ai];
}
}
char** merge(char** left, char** right, char** output, int oi, int lcount, int rcount){
if (lcount > 0 && rcount > 0){
int lmin = findMinimum(left, lcount);
int rmin = findMinimum(right, rcount);
if (strcmp(left[lmin], right[rmin]) < 0){
output[oi] = left[lmin];
removeFromArray(left, lmin, lcount);
lcount--;
}
else {
output[oi] = right[rmin];
removeFromArray(right, rmin, rcount);
rcount--;
}
}
else if (lcount == 0) {
if (rcount == 1) {
output[oi] = right[0];
return output;
} else {
int rmin = findMinimum(right, rcount);
output[oi] = right[rmin];
removeFromArray(right, rmin, rcount);
rcount--;
}
}
else if (rcount == 0) {
if (lcount == 1) {
output[oi] = left[0];
return output;
} else {
int lmin = findMinimum(left, lcount);
output[oi] = left[lmin];
removeFromArray(left, lmin, lcount);
lcount--;
}
}
return merge(left, right, output, ++oi, lcount, rcount);
}
int findMinimum(char** array, int count){
char* minvalue = array[0];
char* currentvalue = minvalue;
int minindex = 0;
for (int i = 1; i < count; i++){
currentvalue = array[i];
if (strcmp(currentvalue, minvalue) < 0){
minvalue = currentvalue;
minindex = i;
}
}
return minindex;
}
void removeFromArray(char** array, int index, int count){
// removes specified index from an array
for (int i = index; i < count; i++){
if (i+1 == count){
array[i] = 0; // this entry will be gone when count decrements
} else {
array[i] = array[i+1];
}
}
}