UVa1615 Highway (贪心,区间选点)

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <cmath>
 4 using namespace std;
 5 
 6 const int maxn = 1e5+5;
 7 
 8 struct Interval {
 9     int l, r;
10     bool operator < (const Interval& rhs) const {
11         return r < rhs.r || (r == rhs.r && l > rhs.l);
12     }
13 } itv[maxn];
14 
15 int L, D, N;
16 
17 int main() {
18     while (scanf("%d%d%d", &L, &D, &N) == 3) {
19         double dis = D;
20         for (int i = 0; i < N; i++) {
21             double a, b; scanf("%lf%lf", &a, &b);
22             double d = sqrt(dis*dis - b*b);
23             itv[i].l = a - d; itv[i].r = a + d;
24         }
25         sort(itv, itv + N);
26         int ans = 0;
27         double curPos = -1e9;
28         for (int i = 0; i < N; i++)
29         if (curPos < itv[i].l) {
30             curPos = itv[i].r < L ? itv[i].r : L;
31             ans++;
32         }
33         printf("%d\n", ans);
34     }
35     return 0;
36 }