题目连接：uva 11722 - Joining with Friend

题目大意：你和朋友乘火车，并且都会路过A市，给定两人可能到达A市的时段，火车会停w，问说两人可以见面的概率。

解题思路：y = x + w 和y = x - w在给定时间内围成的面积除以时间的总面积，就是求面积的时候要分情况处理。

#include 
   
     #include 
    
      #include 
     
       using namespace std; int t1, t2, s1, s2, w; double sum; double solve (int k) { double ret = 0; if (s2 > t2 + k && s1 > t1 + k) { double r = max(t2 + k - s1, 0); ret = sum - r * r / 2; } else if (s2 > t2 + k) { double r = 2 * s2 - t1 - t2 - 2 * k; ret = r * (t2 - t1) / 2; } else if (s1 > t1 + k) { double r = s2 + s1 - 2 * k - 2 * t1; ret = r * (s2 - s1) / 2; } else { double r = max(s2 - k - t1, 0); ret = r * r / 2; } if (k < 0) ret = sum - ret; return ret; } int main () { int cas; scanf("%d", &cas); for (int kcas = 1; kcas <= cas; kcas++) { scanf("%d%d%d%d%d", &t1, &t2, &s1, &s2, &w); sum = 1.0 * (t2 - t1) * (s2 - s1); double ans = solve(w) + solve(-w); printf("Case #%d: %.8lf\n", kcas, 1 - ans / sum); } return 0; }