PAT A 1065. A+B and C (64bit) (20)

题目

Given three integers A, B and C in [-2⁶³, 2⁶³], you are supposed to tell whether A+B > C.

Input Specification:

The first line of the input gives the positive number of test cases, T (<=10).  Then T test cases follow, each consists of a single line containing three integers A, B and C, separated by single spaces.

Output Specification:

For each test case, output in one line "Case #X: true" if A+B>C, or "Case #X: false" otherwise, where X is the case number (starting from 1). 

Sample Input:

3
1 2 3
2 3 4
9223372036854775807 -9223372036854775808 0

Sample Output:

Case #1: false
Case #2: true
Case #3: false

 

需要考A+B虑溢出的问题，可能是上界，也可能是下界。

可以考虑string模拟大数的方法，代码用了一种适用于两个元素的投机方法。

 

代码：

#include <iostream>
using namespace std;

int main()
{
	int n;
	cin>>n;

	long long a,b,c;
	int i,j;
	for(i=0;i<n;i++)	//一种投机取巧的办法，仅适用于两个元素
	{
		cin>>a>>b>>c;
		cout<<"Case #"<<i+1<<": ";
		if(a>0&&b>0&&a+b<a&&a+b<b)	//上越界，必然大于c
			cout<<"true\n";
		else if(a<0&&b<0&&a+b>a&&a+b>b)	//下越界，必然小于c
			cout<<"false\n";
		else if(a+b>c)	//常规比较
			cout<<"true\n";
		else
			cout<<"false\n";
	}

	return 0;
}