Random and Sampling

//递归二分方法
const size_t MAXLEN = 10;
const char TestArr[MAXLEN] = {'A','B','C','D','E','F','G','H','I','J'};

static char RecurArr[MAXLEN]={0};
static int cnt = 0;
void ShuffleArray_Recursive_Tmp(char* arr, int len)
{
    if(cnt > MAXLEN || len <=0){
        return;
    }

    int pos = rand() % len;
    RecurArr[cnt++] = arr[pos];
    if (len==1) return;
    ShuffleArray_Recursive_Tmp(arr, pos);
    ShuffleArray_Recursive_Tmp(arr+pos+1, len-pos-1);
}

void ShuffleArray_Recursive(char* arr, int len)
{
    memset(RecurArr, 0, sizeof(RecurArr));
    cnt=0;
    ShuffleArray_Recursive_Tmp(arr, len);
    memcpy(arr, RecurArr, len);
}

void main()
{
    char temp[MAXLEN]={0};
    for(int i=0; i<5; i++) {
        strncpy(temp, TestArr, MAXLEN);
        ShuffleArray_Recursive((char*)temp, MAXLEN);
    }
}

int compare( const void *a, const void *b )
{
    return rand()%3-1;
}

void ShuffleArray_Sort(char* arr, int len)
{
    qsort( (void *)arr, (size_t)len, sizeof(char), compare );
}

void ShuffleArray_General(char* arr, int len)
{
    const int suff_time = len;
    for(int idx=0; idx<suff_time; idx++) {
        int i = rand() % len;
        int j = rand() % len;
        char temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

void ShuffleArray_Fisher_Yates(char* arr, int len)
{
    int i = len, j;
    char temp;

    if ( i == 0 ) return;
    while ( --i ) {
        j = rand() % (i+1);
        temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

/* Arrange the N elements of ARRAY in random order.
   Only effective if N is much smaller than RAND_MAX;
   if this may not be the case, use a better random
   number generator. */
void shuffle(int *array, size_t n)
{
    if (n > 1) {
        size_t i;
        for (i = 0; i < n - 1; i++) {
          size_t j = i + rand() / (RAND_MAX / (n - i) + 1);
          int t = array[j];
          array[j] = array[i];
          array[i] = t;
        }
    }
}

void ShuffleArray_Manual(char* arr, int len)
{
    int mid = len / 2;

    for (int n=0; n<5; n++){

        //两手洗牌
        for (int i=1; i<mid; i+=2){
            char tmp = arr[i];
            arr[i] = arr[mid+i];
            arr[mid+i] = tmp;
        }

        //随机切牌
        char *buf = (char*)malloc(sizeof(char)*len);

        for(int j=0; j<5; j++) {
            int start= rand() % (len-1) + 1;
            int numCards= rand()% (len/2) + 1;

            if (start + numCards > len ){
                numCards = len - start;
            }

            memset(buf, 0, len);
            strncpy(buf, arr, start);
            strncpy(arr, arr+start, numCards);
            strncpy(arr+numCards, buf, start);
        }
        free(buf);

    }
}