Codeforces 832 C Strange Radiation

题目地址
题意：就是告诉你每个人的位置，速度，以及行进方向，让你求出把一个炸弹放在某个位置上的全部人出去的最短时间，炸弹爆炸产生的冲击波会给相同方向的人应该s的速度使得它的速度为v+s
思路：二分时间，通过时间来求向右和向左的区间，如果区间有交集，就是可以放炸弹，反之则不行。

#include <iostream>#include <cstring>#include <string>#include <queue>#include <vector>#include <map>#include <set>#include <stack>#include <cmath>#include <cstdio>#include <iomanip>//cout << fixed << setprecision(10) << ans << endl;小数#include <algorithm>#define N 100010#define M 510#define LL __int64#define inf 0x3f3f3f3f#define lson l,mid,ans<<1#define rson mid+1,r,ans<<1|1using namespace std;const LL mod = 1e9 + 7;const double eps = 1e-9;int n, s;struct node {    LL x, v, d;}num[N];bool check(double times) {    LL l1 = 1000001, r1 = 0, l2 = 1000001, r2 = 0;    for (int i = 0; i < n; i++) {        if (num[i].d == 1) {            if (num[i].v*times >= num[i].x) {                l1 = 0;                r1 = 1000000;            }            else if ((num[i].v + s)*times >= num[i].x) {                l1 = min(l1, num[i].x);                r1 = max(r1, num[i].x + (LL)((s*times + num[i].v*times - num[i].x)*(s - num[i].v)) / s);            }        }        else {            if (num[i].v*times >= 1000000 - num[i].x) {                l2 = 0;                r2 = 1000000;            }            else if ((num[i].v + s)*times >= 1000000 - num[i].x) {                r2 = max(r2, num[i].x);                l2 = min(l2, num[i].x - (LL)((s*times + num[i].v*times - 1000000 + num[i].x)*(s - num[i].v)) / s);            }        }    }    if (l1 > r2 || l2 > r1) {        return 0;    }    return 1;}int main() {    cin.sync_with_stdio(false);    while (cin >> n >> s) {        for (int i = 0; i < n; i++) {            cin >> num[i].x >> num[i].v >> num[i].d;        }        double l = 0, r = 1000000;        double mid;        double ans;        for (int i = 0; i < 100;i++) {            mid = (l + r) / 2;            if (check(mid)) {                ans = mid;                r = mid - 1;            }            else {                l = mid + 1;            }        }        cout << fixed << setprecision(10) << ans << endl;    }    return 0;}

PS：贴一个错误的二分代码，虽然我不知道为什么是错的，我看了别人的代码那样写才AC了，希望有大佬告诉一下我

double l = 0, r = 1000000;double mid;double ans;while (l < r) {    mid = (l + r) / 2;    if (check(mid)) {        ans = mid;        r = mid - 1;    }    else {        l = mid + 1;    }}