c - 二维字符数组中的排序列

Question

<分区>

Answer 1

这是一种方法:取每个计数，将其左移五位，然后按位或低五位中的字母编号。对生成的数字进行排序，并通过使用 0x1F 并添加 'a' 将其最低有效的五位转换回字母。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int compare (const void * a, const void * b) {
    int ia = *(int*)a;
    int ib = *(int*)b;
    return (ia>>5) == (ib>>5) ? ia-ib : ib-ia;
}

int main(int argc, char* argv[]) {
    char string[100] = "quickbrownfoxjumpsoverthelazydog";
    int c = 0, count[26];
    memset(count, 0, sizeof(count));
    while ( string[c] != '\0' ) {
        if ( string[c] >= 'a' && string[c] <= 'z' ) {
            count[string[c]-'a']++;
        }
        c++;
    }
            // Shift the letter ordinal into the lower five bits of the count*32
    for ( c = 0 ; c < 26 ; c++ ) {
        count[c] = (count[c] << 5) | c;
    }
            // Sort the results using the custom compare function
    qsort(count, 26, sizeof(int), compare);
            // Print the letters by taking the lower five bits
    for ( c = 0 ; c < 26 ; c++ ) {
        printf("%c", 'a'+(count[c]&0x1F));
    }
    printf("\n");
            // Print the counts by ignoring the lower five bits
    for ( c = 0 ; c < 26 ; c++ ) {
        printf("%d", count[c] >> 5);
    }
    return 0;
}