Added SCC : Kosaraju, Tarjan

Author: subinium

README.md

@@ -13,8 +13,6 @@
 
 ## Graph
 
-### ETC
-
 ### Shotest Path
 
 - [Floyd-Warshall](/graph/shortest_path/floyd_warshall.py)
@@ -24,12 +22,20 @@
 - [Bellman-Ford](/graph/shortest_path/bellman_ford.py)
   - [BOJ 11657 : 타임머신](https://www.acmicpc.net/problem/11657)
 
-### MST
+### MST (Minimum Spanning Tree)
 
 - [Kruskal](/graph/mst/kruskal.py)
 - [Prim](/graph/mst/prim.py)
   - [BOJ 1197 : 최소 스패닝 트리](https://www.acmicpc.net/problem/1197)
 
+### SCC (Strongly Connected Component)
+
+- [Kosaraju](/graph/scc/kosaraju.py)
+- [Tarjan](/graph/scc/tarjan.py)
+  - [BOJ 2150 : Strongly Connected Component](https://www.acmicpc.net/problem/2150)
+
+### ETC
+
 ## String
 
 - [KMP](/string/kmp.py)

graph/scc/kosaraju.py

@@ -0,0 +1,52 @@
+# [BOJ 2150] Strongly Connected Component 
+# link : https://www.acmicpc.net/problem/2150
+# tag : graph, SCC, Kosaraju, DFS, stack
+# @subinium
+
+import sys
+sys.setrecursionlimit(10000) # 재귀함수 런타임에러 방지
+
+# Kosaraju 
+def kosaraju(v, edge_raw):
+    stack, scc = [], [[] for _ in range(v+1)]
+    visited = [False for _ in range(v+1)]
+    edge, edge_rev = [[] for _ in range(v+1)], [[] for _ in range(v+1)]
+    for st, ed in edge_raw:
+        edge[st].append(ed)
+        edge_rev[ed].append(st)
+
+    # DFS for stack & reverse
+    def dfs(now, group=0):
+        visited[now] = True
+        if group: scc[group].append(now)
+        for nxt in (edge[now] if group else edge_rev[now]):
+            if not visited[nxt]: dfs(nxt, group)
+        if not group: stack.append(now)
+
+    for i in range(1, v+1):
+        if not visited[i]: dfs(i)
+
+    num_groups = 0
+    visited = [False for _ in range(v+1)]
+
+    for i in stack[::-1]:
+        if not visited[i]:
+            num_groups += 1
+            dfs(i, num_groups)
+
+    return num_groups, scc[1: 1+num_groups]
+
+
+# Main
+if __name__ == '__main__':
+    input = sys.stdin.readline
+    V, E = map(int, input().split())
+    edge = [tuple(map(int, input().split())) for _ in range(E)]
+    num_groups, scc = kosaraju(V, edge)
+    for i in range(num_groups):
+        scc[i].sort()
+        scc[i].append(-1)
+
+    print(num_groups)
+    for group in sorted(scc):
+        print(' '.join(map(str, group)))

graph/scc/tarjan.py

@@ -0,0 +1,55 @@
+# [BOJ 2150] Strongly Connected Component 
+# link : https://www.acmicpc.net/problem/2150
+# tag : graph, SCC, Tarjan, DFS, stack
+# @subinium
+
+import sys
+sys.setrecursionlimit(10000) # 재귀함수 런타임에러 방지
+
+# Tarjan Algorithm 
+def tarjan(v, edge_raw):
+    stack, scc, cnt = [], [], [0] # cnt를 내부함수 전역변수로 쓰기 위해 
+    visited, finished = [0 for _ in range(v+1)], [False for _ in range(v+1)]
+    edge = [[] for _ in range(v+1)]
+    for st, ed in edge_raw: edge[st].append(ed)
+
+    def dfs(now):
+        cnt[0] += 1
+        visited[now] = cnt[0]
+        stack.append(now)
+        result = visited[now]
+
+        for nxt in edge[now]:
+            if visited[nxt] == 0: result = min(result, dfs(nxt))
+            elif not finished[nxt]: result = min(result, visited[nxt])
+
+        if result == visited[now]:
+            group = []
+            while True:
+                top = stack.pop()
+                group.append(top)
+                finished[top] = True
+                if top == now: break
+            scc.append(group)        
+        
+        return result
+
+    for i in range(1, v+1):
+        if visited[i] == 0: dfs(i)
+
+    return len(scc), scc
+
+
+# Main
+if __name__ == '__main__':
+    input = sys.stdin.readline
+    V, E = map(int, input().split())
+    edge = [tuple(map(int, input().split())) for _ in range(E)]
+    num_groups, scc = tarjan(V, edge)
+    for i in range(num_groups):
+        scc[i].sort()
+        scc[i].append(-1)
+
+    print(num_groups)
+    for group in sorted(scc):
+        print(' '.join(map(str, group)))