Codeforces 145A-Lucky Conversion

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

     不得不承認CF上的題確實質量很好，這題還是A題就卡了好一陣，思路很詭異。。

  題意：
       給出一串字符串，只包含數字4和7 然後再給出另一個字符串，同樣是只包含4和7，長度相同，現在給定兩種操作，①：改變a串某位上的數字；②：交換a串任意兩位上的數字，求最小操作數 使得a==b

  因為是要最小操作數，所以要盡可能的執行交換操作，所以 掃一遍a串，看它和b串的對應位置上的數字是不是相同，若不同，記下4和7不同的個數，其中最大數就是答案。

  #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