Nearly Lucky Number

一、Nearly Lucky Number

本题链接：Nearly Lucky Number

题目：

A. Nearly Lucky Number
time limit per test2 seconds
memory limit per test256 megabytes
inputstandard input
outputstandard 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
40047
output
NO

input
7747774
output
YES

input
1000000000000000000
output
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”.

本博客给出本题截图：

题意：有数字7和数字4就是幸运数字，如果一个数中幸运数字的数为7或4的话这个数就是近似幸运数字，如果一个数是近似幸运数字的话就输出YES，反之输出NO

AC代码

#include <iostream>
#include <string>using namespace std;int main()
{
    string a;cin >> a;int sum = 0;for (int i = 0; i < a.size(); i ++ )if (a[i] == '4' || a[i] == '7')sum ++; if (sum == 4 || sum == 7) puts("YES");else puts("NO");return 0;
}

总结

没读清题，以为是输出是否幸运数字，WA了三次
水题，不解释