重复嵌套的for循环应该怎么优化代码

[zhaohuanshia]

这样嵌套的重复代码，有什么方法可以优化吗？

除了for之外，还有什么地方是可以改进优化的吗？

新手一枚，还请大佬们多敲打

[zhouqunhai]

没懂你的意思，你是想优化for的次数，还是迭代？

[zhaohuanshia]

这个for循环明显太重复了

[赵4老师]

百度搜“字典法”

[跑马溜溜的山上]

你是要动态的生成排列组合吧！回溯法。
建议你看看这个文章：
https://blog.csdn.net/goldenhawking/article/details/80037669
Pn,m排列、Cnm组合，级联for循环展开，都可以用类似的思路。文章中最后有级联for的例子。

[跑马溜溜的山上]

#include <vector>
#include <stdio.h>
struct tag_FOR_State
{
	std::vector<unsigned long long> vec_buf;
	std::vector<unsigned long long> vec_bz;
	int swim;
	bool finished;
};

int fnm(const unsigned long long n[/*m*/], int m, std::vector<std::vector <unsigned long long> > & vec_output, tag_FOR_State * state, int limit/* = 0*/)
{
	std::vector<unsigned long long> & vec_buf = state->vec_buf,
		&vec_bz = state->vec_bz;
	int &swim = state->swim;
	bool &finished = state->finished;

	if (vec_bz.size() == 0)
	{
		for (int i = 0; i<m; ++i)    vec_buf.push_back(0);
		vec_bz.push_back(0);
		swim = 0;
		finished = false;
	}

	if (finished == true)
		return 0;
	int group = 0;
	do
	{
		unsigned long long ch = 0;
		if (swim<m)
		{
			vec_buf[swim] = ch;
			++swim;
		}
		if (swim == m)
		{
			vec_output.push_back(vec_buf);
			++group;
			bool hit = false;
			do
			{
				--swim;
				if (swim >= 0)
				{
					unsigned long long nextv = vec_buf[swim];
					do
					{
						++nextv;
						if (nextv >= n[swim])
							break;
						hit = true;
					} while (hit == false);
					if (hit == true)
					{
						vec_buf[swim] = nextv;
						++swim;
					}
				}
				else
					finished = true;
			} while (finished == false && hit == false);
			if (group >= limit && limit>0)
				break;
		}
	} while (finished == false);
	return group;
}

int fnm_next(const unsigned long long n[/*m*/], int m, std::vector<std::vector <unsigned long long> > & vec_output, tag_FOR_State * state, int limit/* = 0*/)
{
	std::vector<unsigned long long> & vec_buf = state->vec_buf,
		&vec_bz = state->vec_bz;
	int &swim = state->swim;
	bool &finished = state->finished;

	if (vec_bz.size() == 0)
	{
		for (int i = 0; i<m; ++i)    vec_buf.push_back(0);
		vec_bz.push_back(0);
		swim = 0;
		finished = false;
	}
	if (finished == true)
		return 0;
	int group = 0;
	do
	{
		unsigned long long ch = 0;
		if (swim<m)
		{
			vec_buf[swim] = ch;
			++swim;
		}
		if (swim == m)
		{
			memcpy(vec_output[group].data(), vec_buf.data(), m * sizeof(unsigned long long));
			++group;
			bool hit = false;
			do
			{
				--swim;
				if (swim >= 0)
				{
					unsigned long long nextv = vec_buf[swim];
					do
					{
						++nextv;
						if (nextv >= n[swim])
							break;
						hit = true;
					} while (hit == false);
					if (hit == true)
					{
						vec_buf[swim] = nextv;
						++swim;
					}
				}
				else
					finished = true;
			} while (finished == false && hit == false);
			if (group >= limit && limit>0)
				break;
		}
	} while (finished == false);
	return group;
}

int main()
{
	tag_FOR_State state;
	const unsigned long long n[] = { 26,26,10,4,10 };
	const int m = sizeof(n)/sizeof(n[0]);
	std::vector<std::vector<unsigned long long> > vec_res;
	int nret = fnm(n, m, vec_res, &state, 1024);
	while (nret)
	{
		for (int i = 0; i < nret; ++i)
			printf("%c%c%c%c%c\r",
				char(vec_res[i][0] + 'a'),
				char(vec_res[i][1] + 'A'),
				char(vec_res[i][2] + '!'),
				char(vec_res[i][3] + '@'),
				char(vec_res[i][4] + '0')
				);
		nret = fnm_next(n, m, vec_res, &state, 1024);
	}
	return 0;
}

[xg436]

递归

#include "stdafx.h"
#include <string>
#define LastIndex 3

char a[] = "ddws";
char b[] = "aaaa";
void Next(int index);

int main()
{
Next(0);
return 0;
}

void Next(int index)
{
if (index > LastIndex)
{
if (strcmp(a, b) == 0)
{
printf("密码是%s", b);
}
return;
}
while (b[index] <= 'z')
{
int i = index;
while (++i <= LastIndex)
{
b[i] = 'a';
}
Next(index + 1);
b[index]++;
}
}

[donjin9]

这样相当于26进制数的递增吧。

#include <string>
#define LEN 4

void main() {
    char pwd[LEN + 1] = "sdfa";
    char str[LEN + 1] = "aaaa";
    while ( str[LEN] <= 'z' && strcmp( str, pwd ) != 0 ) {
        for ( int i = 0; i < LEN; ++i ) {
            if ( ++str[i] > 'z' ) {
                str[i] = 'a';
            }
            else {
                break;
            }
        }
    }
    printf( "%s\n", str );
    getchar();
}

[zhaohuanshia]

引用 6 楼 xg436 的回复:

递归 #include "stdafx.h" #include <string> #define LastIndex 3 char a[] = "ddws"; char b[] = "aaaa"; void Next(int index); int main() { Next(0); return 0; } void Next(int index) { if (index > LastIndex) { if (strcmp(a, b) == 0) { printf("密码是%s", b); } return; } while (b[index] <= 'z') { int i = index; while (++i <= LastIndex) { b[i] = 'a'; } Next(index + 1); b[index]++; } }

while (++i <= LastIndex) 这个为什么用while而不用if呢？