1065. A+B and C (64bit) (20)-PAT甲级真题

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
分析:
因为A、B的大小为[-2^63, 2^63],用long long 存储A和B的值,以及他们相加的值sum:
如果A > 0, B < 0 或者 A < 0, B > 0,sum是不可能溢出的
如果A > 0, B > 0,sum可能会溢出,sum范围理应为(0, 2^64 – 2],溢出得到的结果应该是[-2^63, -2]是个负数,所以sum < 0时候说明溢出了
如果A < 0, B < 0,sum可能会溢出,同理,sum溢出后结果是大于0的,所以sum > 0 说明溢出了