LightOJ 1077 How Many Points?
Description
Given two points A and B on the X-Y plane, output the number of the lattice points on the segment AB. Note that A and B are also lattice point. Those who are confused with the definition of lattice point, lattice points are those points which have both x and y co-ordinate as integer.
For example, for A (3, 3) and B (-1, -1) the output is 5. The points are: (-1, -1), (0, 0), (1, 1), (2, 2) and (3, 3).
Input
Input starts with an integer T (≤ 125), denoting the number of test cases.
Each case contains four integers, Ax, Ay, Bx and By. Each of them will be fit into a 32 bit signed integer.
Output
For each test case, print the case number and the number of lattice points between AB.
Sample Input
2
3 3 -1 -1
0 0 5 2
Sample Output
Case 1: 5
Case 2: 2
题目很简单,就是让你求两个整数点连成的线段上的整数点（包括两端）有多少个比如（1，1）（3，3）之间的点有（1，1），（2，2），（3，3）三个点；
看到这个题我想用斜率来做，结果做了两个小时还是不对，后来才知道思路不对，求下公约数就能出来；
#include<stdio.h>#include<stdlib.h>#include<algorithm>using namespace std;int main(){ int tCase,t=1; long long x1,y1,y2,x2; scanf("%d",&tCase); while(tCase--) { scanf("%lld%lld%lld%lld",&x1,&y1,&x2,&y2); printf("Case %d: %lld\n",t++,(long long)__gcd(abs(y2-y1),abs(x2-x1))+1); } return 0;}