UVA 10250 The Other Two Trees

题目

另两棵树

分析

给正方形对角两点坐标，求另两点坐标。应该是对0前面的正负号要求不高。

代码

#include <stdio.h>

int main(void)
{
    double x1, x2, ax1, ax2;
    double y1, y2, ay1, ay2;
    double a, b;
    while (scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2) != EOF) {
        if (x1 == x2 && y1 == y2) {
            printf("Impossible.\n");
            continue;
        }
        /*
        a + b = y1 - y2;
        a - b = x2 - x1;
        */
        a = ((y1-y2)+(x2-x1))/2;
        b = ((y1-y2)-(x2-x1))/2;
        ax1 = x2 - a;
        ay1 = y2 + b;
        ax2 = x2 + b;
        ay2 = y2 + a;
        printf("%.10lf %.10lf %.10lf %.10lf\n", ax1, ay1, ax2, ay2);
    }
    return 0;
}