JZOJ 5196. 【NOIP2017提高组模拟7.3】B

最新推荐文章于 2019-07-09 20:41:09 发布

转载最新推荐文章于 2019-07-09 20:41:09 发布 · 114 阅读

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原文链接：http://www.cnblogs.com/KingSann/articles/9482221.html

本文深入探讨了点分治算法在解决特定路径长度问题上的应用，通过实例分析，讲解了如何利用该算法统计指定范围内最小路径长度，同时对比了不同优化策略对算法效率的影响。

和JZOJ 4715构成双倍经验……

直接点分治的时候统计长度在$[S,E]$的最小的路径长度就行了……

然后题解十分奇怪……

统计的最点对个数应该是$[S,k]$吧……这个似乎必须是$O(n \log^2 n)$吧……而且再套上二分不就三个\log$了……

不太懂题解的做法……

  1 %:pragma GCC optimize(2)
  2 %:pragma GCC optimize(3)
  3 %:pragma GCC optimize("Ofast")
  4 %:pragma GCC optimize("inline")
  5 %:pragma GCC optimize("-fgcse")
  6 %:pragma GCC optimize("-fgcse-lm")
  7 %:pragma GCC optimize("-fipa-sra")
  8 %:pragma GCC optimize("-ftree-pre")
  9 %:pragma GCC optimize("-ftree-vrp")
 10 %:pragma GCC optimize("-fpeephole2")
 11 %:pragma GCC optimize("-ffast-math")
 12 %:pragma GCC optimize("-fsched-spec")
 13 %:pragma GCC optimize("unroll-loops")
 14 %:pragma GCC optimize("-falign-jumps")
 15 %:pragma GCC optimize("-falign-loops")
 16 %:pragma GCC optimize("-falign-labels")
 17 %:pragma GCC optimize("-fdevirtualize")
 18 %:pragma GCC optimize("-fcaller-saves")
 19 %:pragma GCC optimize("-fcrossjumping")
 20 %:pragma GCC optimize("-fthread-jumps")
 21 %:pragma GCC optimize("-funroll-loops")
 22 %:pragma GCC optimize("-fwhole-program")
 23 %:pragma GCC optimize("-freorder-blocks")
 24 %:pragma GCC optimize("-fschedule-insns")
 25 %:pragma GCC optimize("inline-functions")
 26 %:pragma GCC optimize("-ftree-tail-merge")
 27 %:pragma GCC optimize("-fschedule-insns2")
 28 %:pragma GCC optimize("-fstrict-aliasing")
 29 %:pragma GCC optimize("-fstrict-overflow")
 30 %:pragma GCC optimize("-falign-functions")
 31 %:pragma GCC optimize("-fcse-skip-blocks")
 32 %:pragma GCC optimize("-fcse-follow-jumps")
 33 %:pragma GCC optimize("-fsched-interblock")
 34 %:pragma GCC optimize("-fpartial-inlining")
 35 %:pragma GCC optimize("no-stack-protector")
 36 %:pragma GCC optimize("-freorder-functions")
 37 %:pragma GCC optimize("-findirect-inlining")
 38 %:pragma GCC optimize("-fhoist-adjacent-loads")
 39 %:pragma GCC optimize("-frerun-cse-after-loop")
 40 %:pragma GCC optimize("inline-small-functions")
 41 %:pragma GCC optimize("-finline-small-functions")
 42 %:pragma GCC optimize("-ftree-switch-conversion")
 43 %:pragma GCC optimize("-foptimize-sibling-calls")
 44 %:pragma GCC optimize("-fexpensive-optimizations")
 45 %:pragma GCC optimize("-funsafe-loop-optimizations")
 46 %:pragma GCC optimize("inline-functions-called-once")
 47 %:pragma GCC optimize("-fdelete-null-pointer-checks")
 48 
 49 #include <bits/stdc++.h>
 50 using namespace std;
 51 const int N = 1e5 + 10;
 52 vector<pair<int, int> > g[N];
 53 int n, S, E, ans = 0x3f3f3f3f;
 54 int sz[N], f[N] = { 0x3f3f3f3f }, root, ban[N], size;
 55 
 56 void getrt(int u, int fa) {
 57     sz[u] = 1, f[u] = 0;
 58     for(auto e: g[u]) {
 59         int v = e.first, w = e.second;
 60         if(ban[v] || v == fa) continue;
 61         getrt(v, u);
 62         sz[u] += sz[v], f[u] = max(f[u], sz[v]);
 63     }
 64     f[u] = max(f[u], size - sz[u]);
 65     if(f[u] < f[root]) root = u;
 66 }
 67 
 68 set<int> st;
 69 
 70 void dfs(int u, int fa, int dep, int ty) {
 71     if(ty == 0) {
 72         if(S <= dep && dep <= E) ans = min(ans, dep);
 73         int mn = S - dep;
 74         if(st.size()) {
 75             int mx = * -- st.end();
 76             if(dep + mx >= S) {
 77                 int y = dep + *st.lower_bound(S - dep);
 78                 if(S <= y && y <= E) ans = min(ans, y);
 79             }
 80         }
 81     } else st.insert(dep);
 82     for(auto e: g[u]) {
 83         int v = e.first, w = e.second;
 84         if(ban[v] || v == fa) continue;
 85         dfs(v, u, dep + w, ty);
 86     }
 87 }
 88 
 89 void sol(int u) {
 90     ban[u] = 1;
 91     st.clear();
 92     st.insert(0);
 93     for(auto e: g[u]) {
 94         int v = e.first, w = e.second;
 95         if(ban[v]) continue;
 96         dfs(v, u, w, 0);
 97         dfs(v, u, w, 1);
 98     }
 99     for(auto e: g[u]) {
100         int v = e.first, w = e.second;
101         if(ban[v]) continue;
102         root = 0, size = sz[v];
103         getrt(v, 0), sol(root);
104     }
105 }
106 
107 int main() {
108     scanf("%d%d%d", &n, &S, &E);
109     for(int i = 1, u, v, w ; i < n ; ++ i) scanf("%d%d%d", &u, &v, &w), g[u].push_back( { v, w }), g[v].push_back( { u, w } );
110     size = n, getrt(1, 0), sol(root);
111     if(S <= 0 && 0 <= E) ans = min(ans, 0);
112     printf("%d\n", ans == 0x3f3f3f3f ? -1 : ans);
113 }

JZOJ 5196. 【NOIP2017提高组模拟7.3】B

转载于:https://www.cnblogs.com/KingSann/articles/9482221.html