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Commit 672561f

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Create 3559.Number-of-Ways-to-Assign-Edge-Weights-II.cpp
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using ll = long long;
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const int MAXN = 100005;
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const int LOGN = 17;
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class Solution {
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public:
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vector<pair<int,int>> adj[MAXN];
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int up[MAXN][LOGN+1];
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int depth[MAXN];
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ll distRoot[MAXN];
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void dfs(int cur, int parent)
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{
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up[cur][0] = parent;
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for(auto &[v,w]: adj[cur])
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{
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if(v == parent) continue;
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depth[v] = depth[cur] + 1;
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distRoot[v] = distRoot[cur] + w;
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dfs(v, cur);
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}
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}
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int lca(int a, int b)
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{
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if(depth[a] < depth[b]) swap(a,b);
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int diff = depth[a] - depth[b];
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for(int k = 0; k <= LOGN; k++){
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if(diff & (1<<k)) a = up[a][k];
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}
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if(a == b) return a;
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for(int k = LOGN; k >= 0; k--){
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if(up[a][k] != up[b][k]){
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a = up[a][k];
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b = up[b][k];
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}
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}
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return up[a][0];
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}
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ll dist(int a, int b)
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{
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int c = lca(a,b);
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return distRoot[a] + distRoot[b] - 2*distRoot[c];
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}
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ll stepUp(int u, int k) {
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for (int i=LOGN; i>=0; i--) {
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if ((k>>i)&1) {
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u = up[u][i];
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}
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}
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return u;
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}
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vector<int> assignEdgeWeights(vector<vector<int>>& edges, vector<vector<int>>& queries) {
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int n = edges.size()+1;
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for (auto& edge: edges)
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{
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int u = edge[0], v = edge[1], w = 1;
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adj[u].push_back({v,w});
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adj[v].push_back({u,w});
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}
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depth[1] = 0;
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distRoot[1] = 0;
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dfs(1, 1);
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for(int k = 1; k <= LOGN; k++) {
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for(int v = 1; v <= n; v++) {
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up[v][k] = up[up[v][k-1]][k-1];
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}
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}
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vector<ll>power(n+1);
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ll M = 1e9+7;
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power[0] = 1;
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for (int i=1; i<=n; i++)
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power[i] = power[i-1]*2%M;
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vector<int>rets;
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for (auto&q: queries) {
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int u = q[0], v = q[1];
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int d = dist(u,v);
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if (d==0)
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rets.push_back(0);
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else
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rets.push_back(power[d-1]);
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}
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return rets;
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}
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};

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