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authorYidi <noob999noob999@gmail.com>2024-03-22 12:16:34 +0100
committerYidi <noob999noob999@gmail.com>2024-03-22 12:16:34 +0100
commitf1261bb7cd35840b9b5937a6260308f3839c6f3e (patch)
tree2042f32b7c5b4cec7255e66f32f75640ec529f11 /graph/reroot.cpp
parent9906aa7bbf98bee5cdb91e80f6a2311e43129c7d (diff)
minor (mostly spacing) changes
Diffstat (limited to 'graph/reroot.cpp')
-rw-r--r--graph/reroot.cpp53
1 files changed, 28 insertions, 25 deletions
diff --git a/graph/reroot.cpp b/graph/reroot.cpp
index eeca43e..4c6a748 100644
--- a/graph/reroot.cpp
+++ b/graph/reroot.cpp
@@ -1,39 +1,39 @@
// Usual Tree DP can be broken down in 4 steps:
// - Initialize dp[v] = identity
// - Iterate over all children w and take a value for w
-// by looking at dp[w] and possibly the edge label of v -> w
+// by looking at dp[w] and possibly the edge label of v -> w
// - combine the values of those children
-// usually, this operation should be commutative and associative
-// - finalize the value of dp[v] after iterating over all children
-struct Reroot{
+// usually this operation should be commutative and associative
+// - finalize the dp[v] after iterating over all children
+struct Reroot {
using T = ll;
// identity element
- T E(){}
+ T E() {}
// x: dp value of child
// e: index of edge going to child
- T takeChild(T x, int e){}
- T combine(T x, T y){}
+ T takeChild(T x, int e) {}
+ T comb(T x, T y) {}
// called after combining all dp values of children
- T finalize(T x, int v){}
+ T fin(T x, int v) {}
vector<vector<pair<int, int>>> g;
vector<int> ord, pae;
vector<T> dp;
- T dfs(int v){
+ T dfs(int v) {
ord.push_back(v);
- for(auto [w, e] : g[v]){
+ for (auto [w, e] : g[v]) {
g[w].erase(find(all(g[w]), pair(v, e^1)));
pae[w] = e^1;
- dp[v] = combine(dp[v], takeChild(dfs(w), e));
+ dp[v] = comb(dp[v], takeChild(dfs(w), e));
}
- return dp[v] = finalize(dp[v], v);
+ return dp[v] = fin(dp[v], v);
}
- vector<T> solve(int n, vector<pair<int, int>> edges){
+ vector<T> solve(int n, vector<pair<int, int>> edges) {
g.resize(n);
- for(int i = 0; i < n-1; i++){
+ for (int i = 0; i < n-1; i++) {
g[edges[i].first].emplace_back(edges[i].second, 2*i);
g[edges[i].second].emplace_back(edges[i].first, 2*i+1);
}
@@ -41,19 +41,22 @@ struct Reroot{
dp.assign(n, E());
dfs(0);
vector<T> updp(n, E()), res(n, E());
- for(int v : ord){
+ for (int v : ord) {
vector<T> pref(sz(g[v])+1), suff(sz(g[v])+1);
- if(v != 0) pref[0] = takeChild(updp[v], pae[v]);
- for(int i = 0; i < sz(g[v]); i++){
- pref[i+1] = suff[i] = takeChild(dp[g[v][i].first], g[v][i].second);
- pref[i+1] = combine(pref[i], pref[i+1]);
+ if (v != 0) pref[0] = takeChild(updp[v], pae[v]);
+ for (int i = 0; i < sz(g[v]); i++){
+ auto [u, w] = g[v][i];
+ pref[i+1] = suff[i] = takeChild(dp[u], w);
+ pref[i+1] = comb(pref[i], pref[i+1]);
}
- for(int i = sz(g[v])-1; i >= 0; i--)
- suff[i] = combine(suff[i], suff[i+1]);
- for(int i = 0; i < sz(g[v]); i++)
- updp[g[v][i].first] = finalize(combine(pref[i], suff[i+1]), v);
- res[v] = finalize(pref.back(), v);
+ for (int i = sz(g[v])-1; i >= 0; i--) {
+ suff[i] = comb(suff[i], suff[i+1]);
+ }
+ for (int i = 0; i < sz(g[v]); i++) {
+ updp[g[v][i].first] = fin(comb(pref[i], suff[i+1]), v);
+ }
+ res[v] = fin(pref.back(), v);
}
return res;
}
-}; \ No newline at end of file
+};