Codeforces 145A-Lucky Conversion

Petya loves lucky numbers very much. Everybody knows that lucky numbers are positive integers whose decimal record contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17,467 are not.

Petya has two strings a and b of the same length n. The strings consist only of lucky digits. Petya can perform operations of two types:

• replace any one digit from string a by its opposite (i.e., replace 4 by 7 and 7 by 4);
• swap any pair of digits in string a.

  Petya is interested in the minimum number of operations that are needed to make string a equal to string b. Help him with the task.

  Input

  The first and the second line contains strings a and b, correspondingly. Strings a and b have equal lengths and contain only lucky digits. The strings are not empty, their length does not exceed 105.

  Output

  Print on the single line the single number ― the minimum number of operations needed to convert string ainto string b.

  Sample test(s) input

  47
  74
  

  output

  1
  

  input

  774
  744
  

  output

  1
  

  input

  777
  444
  

  output

  3

     不得不承认CF上的题确实质量很好，这题还是A题就卡了好一阵，思路很诡异。。

  题意：
       给出一串字符串，只包含数字4和7 然后再给出另一个字符串，同样是只包含4和7，长度相同，现在给定两种操作，①：改变a串某位上的数字；②：交换a串任意两位上的数字，求最小操作数 使得a==b

  因为是要最小操作数，所以要尽可能的执行交换操作，所以 扫一遍a串，看它和b串的对应位置上的数字是不是相同，若不同，记下4和7不同的个数，其中最大数就是答案。

  #include 
       
        
  #include 
        
          #include 
         
           #include 
          
            #include 
           
             #include 
            
              using namespace std; #define LL long long const int maxn=100050; char s[maxn],t[maxn]; int main() { while(~scanf("%s%s",s,t)) { int len=strlen(s),cnt1=0,cnt2=0; for(int i=0;i