5196. 【NOIP2017提高组模拟7.3】B
Time Limits: 1000 ms Memory Limits: 262144 KB Detailed Limits
Goto ProblemSet做法:点分治,emmmm,比较接近模板了。
代码如下:
View Code
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <cstdio> 2 #include <cstring> 3 #include <iostream> 4 #include <algorithm> 5 #define N 300007 6 #define LL long long 7 using namespace std; 8 LL n, S, E, ls[N], tot, Ma[N], Size[N], sum, root, Len ; 9 LL d[N], ans; 10 bool v[N]; 11 struct edge 12 { 13 LL to, next, w; 14 }e[N * 2]; 15 struct arr 16 { 17 LL dis; 18 int fa; 19 }a[N]; 20 21 inline void Add(int x, int y, int w) 22 { 23 e[++tot].to = y; 24 e[tot].w = w; 25 e[tot].next = ls[x]; 26 ls[x] = tot; 27 } 28 29 inline void Getroot(int x, int fa) 30 { 31 Ma[x] = 0, Size[x] = 1; 32 for (int i = ls[x]; i; i = e[i].next) 33 { 34 int visit = e[i].to; 35 if (v[visit] || visit == fa) continue; 36 Getroot(visit, x); 37 Size[x] += Size[visit]; 38 Ma[x] = max(Size[visit], Ma[x]); 39 } 40 Ma[x] = max(Ma[x], sum - Size[x]); 41 if (Ma[x] < Ma[root]) root = x; 42 } 43 44 inline void Getval(int x, int fa, int zs) 45 { 46 a[++Len].dis = d[x]; 47 a[Len].fa = zs; 48 for (int i = ls[x]; i; i = e[i].next) 49 { 50 int visit = e[i].to; 51 if (v[visit] || visit == fa) continue; 52 d[visit] = d[x] + e[i].w; 53 if (!zs) Getval(visit, x, visit); 54 else Getval(visit, x, zs); 55 } 56 } 57 58 int cmp(arr x, arr y) 59 { 60 return x.dis < y.dis; 61 } 62 63 inline LL Acu(int x) 64 { 65 Len = 0, d[x] = 0; 66 Getval(x, 0, 0); 67 sort(a + 1, a + Len + 1, cmp); 68 int l = 1, r = Len; 69 for (; l < r; ) 70 { 71 if (a[l].fa == a[r].fa) 72 { 73 if (a[l].dis + a[r - 1].dis < S) l++; 74 else r--; 75 } 76 else 77 { 78 if (a[l].dis + a[r].dis >= S) 79 { 80 ans = min(ans,(LL)(a[l].dis + a[r].dis)); 81 r--; 82 } 83 else l++; 84 } 85 } 86 } 87 88 inline void work(int x) 89 { 90 Acu(x); 91 v[x] = 1; 92 for (int i = ls[x]; i; i = e[i].next) 93 { 94 int visit = e[i].to; 95 if (v[visit]) continue; 96 sum = Size[visit]; 97 root = 0; 98 Getroot(visit, 0); 99 work(root); 100 } 101 } 102 103 int main() 104 { 105 scanf("%d%d%d", &n, &S, &E); 106 memset(v, 0, sizeof(v)); 107 memset(ls, 0, sizeof(ls)); 108 for (int i = 1; i <= n - 1; i++) 109 { 110 int u, v, w; 111 scanf("%d%d%d", &u, &v, &w); 112 Add(u, v, w); 113 Add(v, u, w); 114 } 115 ans = 0x3f3f3f3f; 116 sum = n; 117 Ma[0] = 0x3f3f3f3f; 118 Getroot(1, 0); 119 work(root); 120 if (ans > E) printf("-1"); 121 else printf("%lld", ans); 122 }