最近做题的时候，，经常遇到范围是2^63，取模2^64的这种题目。遇到这种限制条件时就要想到用unsigned long long类型。
可以简洁地声明为typedef unsigned long long ull。这样，如果ull类型的整数溢出了，就相当于取模2^64了。因为ull的范围是[0,2^64-1]。
而ll的范围是[-2^63,2^63-1]，因为有符号的第63位表示“正负”而不表示数值
下面给出几组对比程序来加深印象：
（1）
#define _CRT_SECURE_NO_WARNINGS #include<iostream>#include<algorithm>#include<string>#include<sstream>#include<set>#include<vector>#include<stack>#include<map>#include<queue>#include<deque>#include<cstdlib>#include<cstdio>#include<cstring>#include<cmath>#include<ctime>#include<functional>using namespace std;typedef long long ll;typedef unsigned long long ull;int main(){ll a = ~0LL >> 1;ull b = ~0LL >> 1;cout << a << ' ' << b << endl;}/*输出结果：-1 18446744073709551615*/
（2）
#define _CRT_SECURE_NO_WARNINGS #include<iostream>#include<algorithm>#include<string>#include<sstream>#include<set>#include<vector>#include<stack>#include<map>#include<queue>#include<deque>#include<cstdlib>#include<cstdio>#include<cstring>#include<cmath>#include<ctime>#include<functional>using namespace std;typedef long long ll;typedef unsigned long long ull;int main(){ll a = (1LL << 63) – 1;ull b = (1LL << 63) – 1;cout << a << ' ' << b << endl;cout << a + 1 << ' ' << b + 1 << endl;}/*输出结果：9223372036854775807 9223372036854775807-9223372036854775808 9223372036854775808*/
（3）
#define _CRT_SECURE_NO_WARNINGS #include<iostream>#include<algorithm>#include<string>#include<sstream>#include<set>#include<vector>#include<stack>#include<map>#include<queue>#include<deque>#include<cstdlib>#include<cstdio>#include<cstring>#include<cmath>#include<ctime>#include<functional>using namespace std;typedef long long ll;typedef unsigned long long ull;int main(){ull a = (1LL << 64) – 1;cout << a << ' ' << a + 1 << endl;}/*输出结果：18446744073709551615 0*/
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