简单/明显的方法是使用sprintf 从数字中获取数字字符串。然后，使用strstr查看较小的数字（例如needle）是否包含在较大的数字（例如haystack）中。
创建数字数组是一种类似的方法。
但是……
有一种更直接的方法可能更快（快 6 倍）。
- 计算大于
needle 的10 的幂。 （例如10, 100, 1000 等）。打电话给mod10。
- 计算
haystack % mod10。
- 如果等于
needle，我们就有匹配项。
- 如果不是，请将
haystack 除以 10
- 重复
haystack >= needle
例如，对于2357 35，mod10 将为 100：
2357 % 100 == 57
235 % 100 == 35
对于2365 35，mod10 为 100：
2365 % 100 == 65
236 % 100 == 36
这里有一些测试代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef DEBUG
#define dbgprt(_lvl,_fmt...) \
do { \
if (opt_d >= _lvl) \
printf(_fmt); \
} while (0)
#else
#define dbgprt(_fmt...) \
do { } while (0)
#endif
int opt_d;
int opt_n;
// match_mod10 -- fast/direct
int
match_mod10(int hay,int need)
{
int mod10;
int haymod;
int match = 0;
for (mod10 = 1; mod10 <= need; mod10 *= 10);
dbgprt(2,"mod10=%d\n",mod10);
while (hay >= need) {
haymod = hay % mod10;
dbgprt(2,"hay=%d need=%d haymod=%d\n",hay,need,haymod);
match = (haymod == need);
if (match)
break;
hay /= 10;
}
return match;
}
// match_strstr -- reference implementation
int
match_strstr(int hay,int need)
{
char haybuf[100];
char needbuf[100];
int match;
sprintf(haybuf,"%d",hay);
sprintf(needbuf,"%d",need);
match = (strstr(haybuf,needbuf) != NULL);
return match;
}
void
dotest(int hay,int need)
{
int strflg;
int modflg;
int fail;
// get reference value
if (opt_n)
strflg = 0;
else
strflg = match_strstr(hay,need);
modflg = match_mod10(hay,need);
if (opt_n)
fail = 0;
else
fail = (strflg != modflg);
if (opt_d || fail) {
printf("%d %d -- strflg=%d modflg=%d %s\n",
hay,need,strflg,modflg,fail ? "FAIL" : "PASS");
if (fail)
exit(1);
}
}
int
main(int argc,char **argv)
{
--argc;
++argv;
for (; argc > 0; --argc, ++argv) {
char *cp = *argv;
if (*cp != '-')
break;
cp += 2;
switch (cp[-1]) {
case 'd':
opt_d = (*cp != 0) ? atoi(cp) : 1;
break;
case 'n':
opt_n = ! opt_n;
break;
}
}
do {
int hay;
int need;
if (argc == 2) {
hay = atoi(argv[0]);
need = atoi(argv[1]);
dotest(hay,need);
break;
}
for (need = 2; need <= 99; ++need) {
for (hay = 1; hay < 1000000; ++hay)
dotest(hay,need);
}
printf("FINAL: %d %d\n",hay,need);
} while (0);
return 0;
}
更新：
来自安缦：
有了 Craig Estey 的想法，按照他的想法，你可以在没有数组的情况下轻松编码，并且效率更高。这里我已经写好了函数。
让某人使用和改编为他们的答案编写的代码真是令人高兴。
我决定对各种算法进行基准测试。
虽然 Aman 的适应似乎很快，但实际上它会减慢速度。它比 [reference] strstr 以外的所有其他方法都慢。
我的算法和 Aman 的算法都有相同的最终循环。
但是，mod10 算法使用了一个使用乘法的循环。 Aman 使用了除法[比乘法慢]。
然后，它使用了pow——这是昂贵的。这可以用一个带有乘法的循环来代替，以获得一些加速。
我修改了原始的 mod10 方法以使用 mod10 值的缓存/记忆。这提供了一些进一步的加速
这是基准输出：
HAY: 1 1000000
NEED: 2 99
TESTS: strstr strstr2 array array2 mod10 aman1 aman2 mod10b
Sorted:
23.726686639 strstr -- sprintf/strstr reference
13.021570598 strstr2 (1.822x faster) (1.822x faster) -- sprintf/strstr (cached)
3.827459623 aman1 (3.402x faster) (6.199x faster) -- Aman's original (with pow)
3.265761858 array (1.172x faster) (7.265x faster) -- decode numbers into arrays
2.875820484 array2 (1.136x faster) (8.250x faster) -- arrays (cached)
2.826747834 aman2 (1.017x faster) (8.394x faster) -- Aman's modified (multiply)
1.873383061 mod10 (1.509x faster) (12.665x faster) -- mod10 algorithm
1.803308872 mod10b (1.039x faster) (13.157x faster) -- mod10 (with caching)
这是基准代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#define XFLUSH \
do { \
if (! hangflg) \
break; \
fputc('\n',stdout); \
hangflg = 0; \
} while (0)
int hangflg;
#define dbgok(_lvl) \
_dbgok(#_lvl[0])
#ifdef DEBUG
#define dbgprt(_lvl,_fmt...) \
do { \
if (! dbgok(_lvl)) \
break; \
XFLUSH; \
printf(_fmt); \
} while (0)
#else
#define dbgprt(_fmt...) \
do { } while (0)
#endif
typedef long long tsc_t;
typedef unsigned int u32;
typedef unsigned char byte;
int opt_c;
int opt_q;
byte opt_d[256];
int haylim[2];
int needlim[2];
int mod10b_redo;
int outflg = 1;
#define outprt(_fmt...) \
do { \
if (outflg) \
printf(_fmt); \
} while (0)
static inline byte
_dbgok(int lvl)
{
return opt_d[(byte) lvl];
}
tsc_t
tscget(void)
{
struct timespec ts;
tsc_t tsc;
clock_gettime(CLOCK_MONOTONIC,&ts);
tsc = ts.tv_sec;
tsc *= 1000000000;
tsc += ts.tv_nsec;
return tsc;
}
double
tscsec(tsc_t tsc)
{
double sec;
sec = tsc;
sec /= 1e9;
return sec;
}
// match_mod10 -- fast/direct
int
match_mod10(int hay,int need)
{
int mod10;
int haymod;
int match = 0;
for (mod10 = 1; mod10 <= need; mod10 *= 10);
dbgprt(L,"mod10=%d\n",mod10);
while (hay >= need) {
haymod = hay % mod10;
dbgprt(L,"hay=%d need=%d haymod=%d\n",hay,need,haymod);
match = (haymod == need);
if (match)
break;
hay /= 10;
}
return match;
}
// match_mod10b -- fast/direct (cached)
int
match_mod10b(int hay,int need)
{
static int limlo = 0;
static int limhi = -1;
int mod10;
int haymod;
int match = 0;
if ((need >= limhi) || (need < limlo)) {
limlo = 1;
limhi = 1;
for (mod10 = 1; mod10 <= need;) {
limlo = mod10;
mod10 *= 10;
limhi = mod10;
}
++mod10b_redo;
dbgprt(N,"DEBUG: need=%d mod10=%d limlo=%d limhi=%d mod10b_redo=%d\n",
need,mod10,limlo,limhi,mod10b_redo);
}
mod10 = limhi;
while (hay >= need) {
haymod = hay % mod10;
dbgprt(L,"hay=%d need=%d haymod=%d\n",hay,need,haymod);
match = (haymod == need);
if (match)
break;
hay /= 10;
}
return match;
}
// match_strstr -- reference implementation
int
match_strstr(int hay,int need)
{
char haybuf[100];
char needbuf[100];
int match;
sprintf(haybuf,"%d",hay);
sprintf(needbuf,"%d",need);
match = (strstr(haybuf,needbuf) != NULL);
return match;
}
// match_strstr -- reference implementation (cached)
int
match_strstr2(int hay,int need)
{
static int hayold = -1;
static char haybuf[100];
static int needold = -1;
static char needbuf[100];
int match;
if (hay != hayold) {
sprintf(haybuf,"%d",hay);
hayold = hay;
}
if (need != needold) {
sprintf(needbuf,"%d",need);
needold = need;
}
match = (strstr(haybuf,needbuf) != NULL);
return match;
}
int
_match_array(int hay,char *haybuf)
{
char *hayp;
for (hayp = haybuf; hay != 0; ++hayp) {
*hayp = hay % 10;
hay /= 10;
}
return (hayp - haybuf);
}
// match_array -- array
int
match_array(int hay,int need)
{
int match = 0;
char haybuf[100];
int haylen = _match_array(hay,haybuf);
char needbuf[100];
int needlen = _match_array(need,needbuf);
char *haye = &haybuf[haylen - needlen];
for (char *hayp = haybuf; hayp <= haye; ++hayp) {
for (int needidx = 0; needidx < needlen; ++needidx) {
match = (hayp[needidx] == needbuf[needidx]);
dbgprt(L,"match_array: TRY needidx=%d hayp=%d needbuf=%d match=%d\n",
needidx,hayp[needidx],needbuf[needidx],match);
if (! match)
break;
}
if (match)
break;
}
return match;
}
// match_array2 -- array (cached)
int
match_array2(int hay,int need)
{
int match = 0;
static int hayold = -1;
static int haylen = -1;
static char haybuf[100];
if (hay != hayold) {
haylen = _match_array(hay,haybuf);
hayold = hay;
dbgprt(H,"match_array: HAYSET hay=%d haylen=%d\n",hay,haylen);
}
static int needold = -1;
static int needlen = -1;
static char needbuf[100];
if (need != needold) {
needlen = _match_array(need,needbuf);
needold = need;
dbgprt(N,"match_array: NEEDSET need=%d needlen=%d\n",need,needlen);
}
char *haye = &haybuf[haylen - needlen];
for (char *hayp = haybuf; hayp <= haye; ++hayp) {
for (int needidx = 0; needidx < needlen; ++needidx) {
match = (hayp[needidx] == needbuf[needidx]);
dbgprt(L,"match_array: TRY needidx=%d hayp=%d needbuf=%d match=%d\n",
needidx,hayp[needidx],needbuf[needidx],match);
if (! match)
break;
}
if (match)
break;
}
return match;
}
#if 0
typedef u32 arg_t;
#else
typedef int arg_t;
#endif
int
match_aman1(arg_t a, arg_t b)
{
int temp, b_size = 0, tens = 1;
temp = b;
// finding total digits in b
while (temp) {
b_size++;
temp /= 10;
}
tens = pow(10, b_size);
while (a) {
if ((a % tens) == b)
return 1;
a /= 10;
}
return 0;
}
int
match_aman2(arg_t a, arg_t b)
{
int temp, b_size = 0, tens = 1;
temp = b;
// finding total digits in b
while (temp) {
b_size++;
temp /= 10;
}
#if 0
tens = pow(10, b_size);
#else
for (; b_size > 0; --b_size)
tens *= 10;
#endif
while (a) {
if ((a % tens) == b)
return 1;
a /= 10;
}
return 0;
}
typedef struct {
int (*tst_fnc)(int hay,int need);
const char *tst_tag;
const char *tst_reason;
int tst_enable;
tsc_t tst_elap;
} tst_t;
typedef tst_t *tst_p;
typedef const tst_t *tst_pc;
#define TST(_fnc,_reason) \
{ \
.tst_fnc = _fnc, \
.tst_tag = #_fnc, \
.tst_reason = _reason, \
.tst_enable = 1 \
}
tst_t tstlist[] = {
TST(match_strstr,"sprintf/strstr reference"),
TST(match_strstr2,"sprintf/strstr (cached)"),
TST(match_array,"decode numbers into arrays"),
TST(match_array2,"arrays (cached)"),
TST(match_mod10,"mod10 algorithm"),
TST(match_aman1,"Aman's original (with pow)"),
TST(match_aman2,"Aman's modified (multiply)"),
TST(match_mod10b,"mod10 (with caching)"),
{ .tst_tag = NULL }
};
#define TSTFORALL(_tst) \
_tst = tstlist; _tst->tst_tag != NULL; ++_tst
const char *
tagof(tst_pc tstcur)
{
const char *cp;
const char *tag;
tag = tstcur->tst_tag;
cp = strrchr(tag,'_');
if (cp != NULL)
tag = cp + 1;
return tag;
}
void
dochk(int hay,int need)
{
tst_p tstcur;
tst_p tstold = NULL;
int oldflg;
int curflg;
int fail;
for (TSTFORALL(tstcur)) {
curflg = tstcur->tst_fnc(hay,need);
if (tstold == NULL) {
tstold = tstcur;
oldflg = curflg;
}
fail = (curflg != oldflg);
if (dbgok(C) || fail) {
if (fail)
XFLUSH;
printf("%d %d -- %s=%d %s=%d %s\n",
hay,need,
tagof(tstold),oldflg,
tagof(tstcur),curflg,
fail ? "FAIL" : "PASS");
if (fail)
exit(1);
}
tstold = tstcur;
oldflg = curflg;
}
}
void
dochkall(void)
{
int hay;
hay = haylim[0];
mod10b_redo = 0;
for (int iter = 1; iter <= 10; ++iter) {
for (int need = needlim[0]; need <= needlim[1]; ++need)
dochk(hay,need);
}
tsc_t tscbeg = tscget();
mod10b_redo = 0;
for (int need = needlim[0]; need <= needlim[1]; ++need) {
printf("\rneed: %d ",need);
hangflg = 1;
fflush(stdout);
for (hay = haylim[0]; hay <= haylim[1]; ++hay)
dochk(hay,need);
}
tsc_t tscend = tscget();
tscend -= tscbeg;
XFLUSH;
printf("ELAPSED: %.9f\n",tscsec(tscend));
}
void
dorat(double elap,tsc_t tscold)
{
double ratio = tscsec(tscold);
const char *tag;
ratio /= elap;
if (ratio < 1.0) {
tag = "slower";
ratio = 1.0 / ratio;
}
else
tag = "faster";
outprt(" (%.3fx %s)", ratio,tag);
}
int
tstcmp(const void *vplhs,const void *vprhs)
{
tst_pc tstlhs = vplhs;
tst_pc tstrhs = vprhs;
tsc_t dif;
int cmp;
dif = tstrhs->tst_elap - tstlhs->tst_elap;
cmp = 0;
if (dif < 0)
cmp = -1;
if (dif > 0)
cmp = 1;
dbgprt(D,"tstcmp: DIF %.9f %.9f dif=%lld cmp=%d\n",
tscsec(tstrhs->tst_elap),tscsec(tstlhs->tst_elap),dif,cmp);
return cmp;
}
int ratflg;
void
dotsc(tst_p tstcur)
{
tsc_t tscelap = tstcur->tst_elap;
static tsc_t tscref;
static tsc_t tscold;
if (! ratflg) {
tscref = tscelap;
tscold = tscelap;
}
double elap = tscsec(tscelap);
outprt("%.9f %s",elap,tagof(tstcur));
if (ratflg) {
dorat(elap,tscold);
dorat(elap,tscref);
}
ratflg = 1;
if (tstcur->tst_reason != NULL)
outprt(" -- %s",tstcur->tst_reason);
outprt("\n");
tscold = tscelap;
}
void
dotscall(void)
{
tst_p tstcur;
tsc_t tscelap;
outflg = ! opt_q;
outprt("\n");
outprt("Unordered:\n");
ratflg = 0;
for (TSTFORALL(tstcur)) {
tsc_t tscbeg = tscget();
for (int need = needlim[0]; need <= needlim[1]; ++need) {
for (int hay = haylim[0]; hay <= haylim[1]; ++hay)
tstcur->tst_fnc(hay,need);
}
tscelap = tscget();
tscelap -= tscbeg;
tstcur->tst_elap = tscelap;
dotsc(tstcur);
}
int tstcnt = 0;
for (TSTFORALL(tstcur), ++tstcnt);
qsort(tstlist,tstcnt,sizeof(tst_t),tstcmp);
outflg = 1;
outprt("\n");
outprt("Sorted:\n");
ratflg = 0;
for (TSTFORALL(tstcur))
dotsc(tstcur);
}
void
rangeget(char *cp,int *lim)
{
lim[0] = -1;
lim[1] = -1;
lim[0] = strtol(cp,&cp,10);
if (*cp++ == ',')
lim[1] = strtol(cp,&cp,10);
else
lim[1] = lim[0];
}
void
tstopt(char *bp)
{
static int initflg = 1;
tst_p tstcur;
char *cp;
char **av;
char *argv[100];
int negflg;
av = argv;
while (1) {
cp = strtok(bp,",");
*av = cp;
if (cp == NULL)
break;
bp = NULL;
++av;
}
if (initflg) {
initflg = 0;
negflg = 0;
for (av = argv; *av != NULL; ++av) {
if (strchr(*av,'-') != NULL) {
negflg = 1;
break;
}
}
for (TSTFORALL(tstcur))
tstcur->tst_enable = negflg;
}
for (av = argv; *av != NULL; ++av) {
bp = *av;
cp = strrchr(bp,'-');
negflg = (cp != NULL);
if (negflg)
*cp = 0;
for (TSTFORALL(tstcur)) {
const char *tag = tagof(tstcur);
if (strcmp(tag,bp) == 0) {
tstcur->tst_enable = ! negflg;
break;
}
}
}
}
void
dbgopt(char *bp)
{
if (*bp == 0) {
memset(opt_d,1,sizeof(opt_d));
printf("dbgopt: enable all\n");
}
for (; *bp != 0; ++bp) {
opt_d[(byte) *bp] = 1;
printf("dbgopt: enable %c\n",*bp);
}
}
int
main(int argc,char **argv)
{
--argc;
++argv;
for (; argc > 0; --argc, ++argv) {
char *cp = *argv;
if (*cp != '-')
break;
cp += 2;
switch (cp[-1]) {
case 'c': // check mode
opt_c = ! opt_c;
break;
case 'd':
dbgopt(cp);
break;
case 'q':
opt_q = ! opt_q;
break;
case 'T':
tstopt(cp);
break;
}
}
do {
if (argc == 2) {
rangeget(argv[0],haylim);
rangeget(argv[1],needlim);
break;
}
rangeget("1,1000000",haylim);
rangeget("2,99",needlim);
} while (0);
printf("HAY: %d %d\n",haylim[0],haylim[1]);
printf("NEED: %d %d\n",needlim[0],needlim[1]);
printf("TESTS:");
tst_p tstrhs;
tst_p tstlhs = tstlist;
for (TSTFORALL(tstrhs)) {
if (! tstrhs->tst_enable)
continue;
printf(" %s",tagof(tstrhs));
if (tstlhs != tstrhs)
*tstlhs = *tstrhs;
++tstlhs;
}
printf("\n");
tstlhs->tst_tag = NULL;
do {
if (! opt_c) {
dotscall();
break;
}
dochkall();
} while (0);
dbgprt(N,"DEBUG: mod10b_redo=%d\n",mod10b_redo);
return 0;
}