Create 1684-Giant Pizza.cpp

  2SAT problem
  https://cses.fi/book/book.pdf
  page no - 160-162

Author: manitajay

cses graph/1684-Giant Pizza.cpp

@@ -0,0 +1,138 @@
+// JAI BAJARANG BALI
+
+// manitianajay45
+
+// give me some sunshine, give me some rain , give me another chance to grow up once again....
+
+// sab moh maya hai....
+
+/* 
+  2SAT problem
+  https://cses.fi/book/book.pdf
+  page no - 160-162
+/*
+
+
+
+#include <bits/stdc++.h>
+using namespace std;
+
+#define ll long long
+#define mod 1000000007
+ll n,m;
+
+bool visited[200005][2];
+string ans(200005,'*');
+vector<pair<ll,ll>> graph[200005][2];
+vector<pair<ll,ll>> order;
+vector<pair<ll,ll>> graphr[200005][2];
+ll vis[200005][2];
+ll an=0;
+
+
+void topo(ll v,ll tp){
+    visited[v][tp]=true;
+    for(auto u:graph[v][tp]){
+        if(!visited[u.first][u.second]){
+            topo(u.first,u.second);
+        }
+    }
+    order.push_back({v,tp});
+}
+bool flag=true;
+
+void dfs(ll v,ll tp){
+
+
+    if(tp==0 && vis[v][1]==an){
+        flag=false;
+    }
+    if(tp==1 && vis[v][0]==an){
+        flag=false;
+    }
+    vis[v][tp]=an;
+    if(ans[v]=='*'){
+        if(tp==0){
+            ans[v]='+';
+        }else{
+            ans[v]='-';
+        }
+    }
+    
+    for(auto u:graphr[v][tp]){
+        if(vis[u.first][u.second]==0){
+            dfs(u.first,u.second);
+        }
+    }
+
+}
+
+
+
+int main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+
+    // ll n;
+    cin >> n>>m;
+
+    for (ll i = 0; i <n; i++)
+    {
+        ll u,v;
+        char ui,vi;
+        cin>>ui>>u>>vi>>v;
+
+        ll fui,fvi;
+        fui=(ui=='+')?1:0;
+        fvi=(vi=='+')?1:0;
+        if(fui==0){
+            graph[u][1].push_back({v,fvi});
+            graphr[v][fvi].push_back({u,1});
+        }else{
+            graph[u][0].push_back({v,fvi});
+            graphr[v][fvi].push_back({u,0});
+        }
+        if(fvi==0){
+            graph[v][1].push_back({u,fui});
+            graphr[u][fui].push_back({v,1});
+        }else{
+            graph[v][0].push_back({u,fui});
+            graphr[u][fui].push_back({v,0});
+        }
+        
+       
+    }
+    for(ll i=1;i<=m;i++){
+        if(!visited[i][0]){
+            topo(i,0);
+        }
+        if(!visited[i][1]){
+            topo(i,1);
+        }
+    }
+
+    reverse(order.begin(),order.end());
+    
+    for(auto i:order){
+        if(vis[i.first][i.second]==0){
+            an++;
+            dfs(i.first,i.second);
+            if(!flag){
+                break;
+            }
+            // an++;
+        }
+    }
+    if(!flag){
+        cout<<"IMPOSSIBLE"<<endl;
+        return 0;
+    }
+    for(ll i=1;i<=m;i++){
+        cout<<ans[i];
+    }
+    cout<<endl;
+    
+
+    return 0;
+}