贪心 Codeforces Round #288 (Div. 2) B. Anton and currency you all know

题目传送门

 /*
     题意：从前面找一个数字和末尾数字调换使得变成偶数且为最大
     贪心：考虑两种情况：1. 有偶数且比末尾数字大(flag标记)；2. 有偶数但都比末尾数字小(x位置标记)
     仿照别人写的，再看自己的代码发现有清晰的思维是多重要
 */
 #include <cstdio>
 #include <iostream>
 #include <algorithm>
 #include <cmath>
 #include <cstring>
 #include <map>
 using namespace std;

 const int MAXN = 1e5 + ;
 const int INF = 0x3f3f3f3f;
 char s[MAXN];

 int main(void)        //Codeforces Round #288 (Div. 2) B. Anton and currency you all know
 {
     #ifndef ONLINE_JUDGE
         freopen ("B.in", "r", stdin);
     #endif

     scanf ("%s", &s);

     int len = strlen (s);
     bool flag = false;
     int x = -;
     for (int i=; i<len-; ++i)
     {
         if ((s[i] - '') %  == )
         {
             x = i;
             if (s[i] < s[len-])
             {
                 swap (s[i], s[len-]);
                 flag = true;    break;
             }
         }
     }

     if (!flag)
     {
         swap (s[x], s[len-]);
     }
     (x != -) ? printf ("%s\n", s) : puts ("-1");

     return ;
 }

 if (len == )
     {
         puts ("-1");
     }
     else if (len == )
     {
         if ((s[] - '') %  != )    puts ("-1");
         else
         {
             printf ("%c%c\n", s[], s[]);
         }
     }
     else if (len == )
     {
         if ((s[] - '') %  == )
         {
             if ((s[] - '') %  == )
             {
                 if (s[] > s[])    swap (s[], s[]);
                 else    swap (s[], s[]);
                 printf ("%s\n", s);
             }
             else
             {
                 swap (s[], s[]);
                 printf ("%s\n", s);
             }
         }
         else if ((s[] - '') %  == )
         {
             swap (s[], s[]);
             printf ("%s\n", s);
         }
         else    puts ("-1");
     }
     else
     {
         char ch = '';    int x = -;
         for (int i=len-; i>=; --i)
         {
             if ((s[i]-'') %  == )
             {
                 if (ch <= s[i])
                 {
                     if (ch == s[i])
                     {
                         if (s[i] < s[len-])
                         {
                             ch = s[i];     x = i;
                         }
                     }
                     else
                     {
                         ch = s[i];     x = i;
                     }
                 }
             }
         }
         if (x == -)    puts ("-1");
         else
         {
             swap (s[x], s[len-]);
             printf ("%s\n", s);
         }
     }

思维混乱的代码