Applied Algorithms - Chapter 6.1 (HUST) Thầy Phạm Quang Dũng

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Applied Algorithms - (HUST) GV.Phạm Quang Dũng

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第 1 页

goupee.vn goupee.com THUẬT TOÁN ỨNG DỤNG Tarjan DFS algorithm for finding Bridges and Articulation Points cuu duong than cong . com Phạm Quang Dũng Bộ môn KHMT dungpq@soict.hust.edu.vn 1 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 2 页

goupee.vn goupee.com Duyệt theo chiều sâu  Cây DFS  DFS xuất phát từ một đỉnh cho phép thăm các đỉnh con cháu của nó trên cây DFS  Cấu trúc dữ liệu duy trì  num[v]: thời điểm đỉnh v được thăm  low[v]: giá trị num nhỏ nhất của các đỉnh x sao cho có cạnh ngược (u,x) với u là 1 đỉnh con cháu nào đó của v cuu duong than cong . com 2 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 3 页

goupee.vn goupee.com DFS(6) 6 1 4 3 2 8 5 cuu duong than cong . com 9 7 3 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 4 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 cuu duong than cong . com 4 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 5 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 cuu duong than cong . com 5 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 6 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 3 cuu duong than cong . com 6 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 7 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 3 2 cuu duong than cong . com 7 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 8 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 2 8 cuu duong than cong . com 8 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 9 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = 6 2 8 5 cuu duong than cong . com 9 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 10 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = 6 num[9] = 7, low[9] = 7 2 8 5 cuu duong than cong . com 9 10 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 11 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = 6 num[9] = 7, low[9] = num[2] = 4 2 8 5 cuu duong than cong . com 9 11 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 12 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = 6 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = 8 8 5 cuu duong than cong . com 9 7 12 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 13 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = 6 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 8 5 cuu duong than cong . com 9 7 13 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 14 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = 5 3 num[5] = 6, low[5] = low[9] = 4 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 8 5 cuu duong than cong . com 9 7 14 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 15 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = 3 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = low[5] = 4 3 num[5] = 6, low[5] = low[9] = 4 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 8 5 cuu duong than cong . com 9 7 15 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 16 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = 2 1 num[3] = 3, low[3] = num[6] = 1 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = low[5] = 4 3 num[5] = 6, low[5] = low[9] = 4 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 8 5 cuu duong than cong . com 9 7 16 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 17 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = low[3] = 1 1 num[3] = 3, low[3] = num[6] = 1 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = low[5] = 4 3 num[5] = 6, low[5] = low[9] = 4 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 8 5 cuu duong than cong . com 9 7 17 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 18 页

goupee.vn goupee.com DFS(6) 6 num[6] = 1, low[6] = 1 num[1] = 2, low[[1] = low[3] = 1 1 num[3] = 3, low[3] = num[6] = 1 4 num[2] = 4, low[2] = 4 num[8] = 5, low[8] = low[5] = 4 3 num[5] = 6, low[5] = low[9] = 4 num[9] = 7, low[9] = num[2] = 4 2 num[7] = 8, low[7] = num[8] = 5 num[4] = 9, low[4] = 9 8 5 cuu duong than cong . com 9 7 18 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 19 页

goupee.vn goupee.com Sample code #include <bits/stdc++.h> using namespace std; const int N = 10000; int n,m; vector<int> A[N]; bool visited[N]; int num[N]; int low[N]; int t; vector<pair<int,int> > bridges; void input(){ ios_base::sync_with_stdio(0); cin.tie(0); cin >> n >> m; for(int i = 1; i <= m; i++){ int u,v; cin >> u >> v;cuu duong than cong . com A[u].push_back(v); A[v].push_back(u); } } 19 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

第 20 页

goupee.vn goupee.com Sample code void dfs(int s, int ps){ // DFS from s with ps is the parent of s in the DFS tree t++; num[s] = t; low[s] = num[s]; visited[s] = true; for(int i = 0;i < A[s].size(); i++){ int v = A[s][i]; if(v == ps) continue; if(visited[v]){ low[s] = min(low[s],num[v]); }else{ dfs(v,s); low[s] = min(low[s],low[v]); if(low[v] > num[s]){ // discover a bridge (s,v)cuu duong than cong . com bridges.push_back(make_pair(s,v)); } } } } 20 fb.com/goupee.vn CuuDuongThanCong.com https://fb.com/tailieudientucntt

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