11722-joining with friend (probability)

Question connection: Ultraviolet A 11722-joining with friend

You and your friends take the train and all pass by city a. Given the time when the two may arrive at City A, the train will stop at W and ask about the probability of two people meeting each other.

Solution: divide the area enclosed by X + W and Y = x-W in a given time by the total area of the time, which means that the area should be divided into different situations.

#include <cstdio>#include <cstring>#include <algorithm>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;}