UVa 140 - Bandwidth

全排列，统计记录每个排列中“带宽”最大的值，最后输出所有最大值中最小的那个。

代码如下：

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
using namespace std;

int cct, ahl[27], map[27][27];
int save[9], node[9];
char a[500];
int main()
{
#ifdef test
freopen("sample.txt", "r", stdin);
#endif
int len, c, _max;
while(gets(a))
{
if(!strcmp(a, "#"))
break;
_max =10;
cct = 0;
len = strlen(a);
memset(map, 0, sizeof(map));
memset(ahl, 0, sizeof(ahl));
for(int i = 0, flag = 0; i < len; i++)
{
if(a[i] >= 'A' && a[i] <= 'Z')
ahl[a[i] - 'A'] = 1;
if(a[i] == ':')
{
c = a[i - 1] - 'A';
flag = 1;
}
else if(flag && a[i] >= 'A' && a[i] <= 'Z')
map[a[i] - 'A'][c] = map[c][a[i] - 'A'] = 1;
else if(a[i] == ';')
flag = 0;
}
for(int i = 0; i < 26; i++)
if(ahl[i])
node[cct++] = i;
do
{
int num = 0;
for(int i = 0; i < cct; i++)
for(int j = i + 1; j < cct; j++)
if(map[node[i]][node[j]])
if(abs(i - j) > num)
num = abs(i - j);
if(_max > num)
{
_max = num;
memcpy(save, node, sizeof(node));
}
}
while(next_permutation(node, node + cct));
for(int i = 0; i < cct; i++)
printf("%c ", save[i] + 'A');
printf("-> %d\n", _max);
}
return 0;
}

剪枝版：

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
using namespace std;

int cct, ahl[27], map[27][27];
int save[9], node[9];
char a[500];
int main()
{
#ifdef test
freopen("sample.txt", "r", stdin);
#endif
int len, c, _max;
while(gets(a))
{
if(!strcmp(a, "#"))
break;
_max =10;
cct = 0;
len = strlen(a);
memset(map, 0, sizeof(map));
memset(ahl, 0, sizeof(ahl));
for(int i = 0, flag = 0; i < len; i++)
{
if(a[i] >= 'A' && a[i] <= 'Z')
ahl[a[i] - 'A'] = 1;
if(a[i] == ':')
{
c = a[i - 1] - 'A';
flag = 1;
}
else if(flag && a[i] >= 'A' && a[i] <= 'Z')
map[a[i] - 'A'][c] = map[c][a[i] - 'A'] = 1;
else if(a[i] == ';')
flag = 0;
}
for(int i = 0; i < 26; i++)
if(ahl[i])
node[cct++] = i;
do
{
int num = 0;
for(int i = 0; i < cct; i++)
{
for(int j = i + 1; j < cct; j++)
{
if(map[node[i]][node[j]])
if(abs(i - j) > num)
num = abs(i - j);

}
if(num > _max) // 剪枝，num>_max时，直接跳出不用继续往下判断
break;
}
if(_max > num)
{
_max = num;
memcpy(save, node, sizeof(node));
}
}
while(next_permutation(node, node + cct));
for(int i = 0; i < cct; i++)
printf("%c ", save[i] + 'A');
printf("-> %d\n", _max);
}
return 0;
}