A. Nearly Lucky Number

110A
A. Nearly Lucky Number
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.
Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number n is a nearly lucky number.
Input
The only line contains an integer n (1 ≤ n ≤ 1018).
Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is preferred to use the cin, cout streams or the %I64d specificator.
Output
Print on the single line “YES” if n is a nearly lucky number. Otherwise, print “NO” (without the quotes).
Examples
input
Copy
40047
output
Copy
NO
input
Copy
7747774
output
Copy
YES
input
Copy
1000000000000000000
output
Copy
NO
Note
In the first sample there are 3 lucky digits (first one and last two), so the answer is “NO”.
In the second sample there are 7 lucky digits, 7 is lucky number, so the answer is “YES”.
In the third sample there are no lucky digits, so the answer is “NO”.
错误理解：这种思路纯属没看清题，题目让求的是类幸运数，而不是幸运数
求幸运数代码，不是本题的代码

#include<bits/stdc++.h>
using namespace std;
int main()
{
    
    
  char a[1000];
  int flag=1;
    gets(a);
    int l=strlen(a);
    for(int i=0;i<l;i++)
    {
    
    
        if(a[i]=='4'||a[i]=='7') 
            flag=1;
        else{
    
    
          flag=0;
          break;
        }
    }
    if(flag)
       printf("YES\n");
    else
       printf("NO\n");
    
   //    system("pause");
    return 0;
}

正确程序：

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
// Nearly Lucky Number
int main()
{
    
    
   int cnt=0;
   string s;	cin>>s; 
	for(int i=0;i<s.length();i++)
		if(s[i]=='4'||s[i]=='7')cnt++;
	if(cnt==4 || cnt==7)cout<<"YES";
 	else cout<<"NO";
	return 0;
} 

测试点4：
Test: #4, time: 30 ms., memory: 0 KB, exit code: 0, checker exit code: 0, verdict: OK
Input
7
Output
NO
Answer
NO
Checker Log
ok NO
这个测试点用来区分幸运数和类幸运数的
所以本题应看清题意