[CF从零单排#16]110A - Nearly Lucky Number
题目来源:http://codeforces.com/problemset/problem/110/A
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".
题目大意:
这题题目意思不是太清晰,真实的题意应该是这样:4,7都是幸运数字,如果一个数所有数字都是幸运数字,那么这个数是幸运数。一个数中,如果幸运数字的个数是幸运数,那么这个数叫做类幸运数。问某个数是否为类幸运数。
题目分析:
题意清晰后,本题就是很简单的模拟题。因为题目提示数字可能是longlong,那么数字个数最多是64,因此存在的幸运数只有4,7,47。所以只需要统计有多少个幸运数,再判定它们是否等于4,7,47即可。
参考代码:
#include <bits/stdc++.h>
using namespace std;
int main(){
long long x;
cin >> x;
int cnt = 0;
while(x){
int t = x%10;
if(t==4 || t==7){
cnt ++;
}
x /= 10;
}
if(cnt==4 || cnt==7 || cnt == 47)
cout << "YES";
else
cout << "NO";
return 0;
}