added solutions by MachangDoniel

1. Flip Columns/7.cpp

@@ -0,0 +1,72 @@
+// Solution with Bitmasking
+#include <cmath>
+#include <cstdio>
+#include <vector>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+
+int n,m,k,ans;
+vector<vector<int>>mat;
+
+void print(){
+    cout<<"mat: "<<endl;
+    for(int i=0;i<n;i++){
+        for(int j=0;j<m;j++){
+            cout<<mat[i][j]<<" ";
+        }
+        cout<<endl;
+    }
+}
+
+void flip(int index){
+    for(int i=0;i<n;i++){
+        mat[i][index]^=1;
+    }
+}
+
+void check(int mask,int k){
+    // cout<<"mask: "<<mask<<" "<<k<<endl;
+    if(k==0){
+        // print();
+        int count=0;
+        for(int i=0;i<n;i++){
+            bool flag=true;
+            for(int j=0;j<m;j++){
+                if(mat[i][j]==0) flag=false;
+            }
+            if(flag) count++;
+        }
+        ans=max(count,ans);
+        // cout<<"ans: "<<ans<<endl;
+        return;
+    }
+    else{
+        for(int j=0;j<m;j++){
+            // if((mask & (1<<j))==0){
+                flip(j);
+                check(mask|(1<<j),k-1);
+                flip(j);
+            // }
+        }
+    }
+}
+
+int main() {
+    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
+    cin>>n>>m>>k;
+    mat.resize(n,vector<int>(m));
+    for(int i=0;i<n;i++){
+        for(int j=0;j<m;j++){
+            cin>>mat[i][j];
+        }
+    }
+    ans=0;
+    for(int j=0;j<m;j++){
+        flip(j);
+        check(1<<j,k-1);
+        flip(j);
+    }
+    cout<<ans<<endl;
+    return 0;
+}

10. Sum of kth level Nodes/2.cpp

@@ -0,0 +1,47 @@
+// Tricky Solution
+#include <cmath>
+#include <cstdio>
+#include <vector>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+
+
+int sToi(string node){
+    int value=0;
+    for(int i=node.size()-1,mul=1;i>=0;i--,mul*=10){
+        value+=(node[i]-'0')*mul;
+    }
+    return value;
+}
+
+
+int main() {
+    /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 
+    int k;
+    string s;
+    vector<vector<int>>v(10);
+    cin>>k>>s;
+    int count=-1;
+    string node;
+    for(int i=0;i<int(s.size());i++){
+        if('0'<=s[i] && s[i]<='9'){
+            node+=s[i];
+        }
+        else{
+            if(!node.empty()){
+                int value=sToi(node);
+                v[count].push_back(value);
+            }
+            node.clear();
+            if(s[i]=='(') count++;
+            else if(s[i]==')') count--;
+        }
+    }
+    int sum=0;
+    for(int i=0;i<int(v[k].size());i++){
+        sum+=v[k][i];
+    }
+    cout<<sum<<endl;
+    return 0;
+}

11. Detect Cycle in Directed Graph/1.cpp

@@ -0,0 +1,167 @@
+#include <cmath>
+#include <cstdio>
+#include <vector>
+#include <iostream>
+#include <algorithm>
+#include<cstring> // extra added
+using namespace std;
+
+#define pb push_back
+#define pp pop_back
+
+// // solution 1
+// int n,m,adj[11][11],stack[11],ans[11],idx,minCycleSum=200005;
+// int vis[11];
+
+// void detectCycle1(int node,int index){
+//     if(vis[node]){
+//         int sum=node;
+//         for(int i=index-2;i>=0 && stack[i]!=node;i--){
+//             sum+=stack[i];
+//         }
+//         if(sum<minCycleSum){
+//             idx=0;
+//             ans[idx++]=node;
+//             for(int i=index-2;i>=0 && stack[i]!=node;i--){
+//                 ans[idx++]=stack[i];
+//             }
+//         }
+//         return;
+//     }
+//     else{
+//         vis[node]=1;
+//         for(int i=1;i<=n;i++){
+//             if(adj[node][i]==1){
+//                 stack[index]=i;
+//                 detectCycle1(i,index+1);
+//             }
+//         }
+//         vis[node]=0;
+//     }
+// }
+
+// void solve1(){
+//     cin>>n>>m;
+//     memset(&adj[0][0],0,(n+1)*(n+1)*sizeof(int));
+//     memset(vis,0,(n+1)*sizeof(int));
+//     for(int i=0;i<m;i++){
+//         int u,v; cin>>u>>v;
+//         adj[u][v]=1;
+//     }
+//     for(int i=1;i<=n;i++){
+//         stack[0]=i;
+//         detectCycle1(i,1);
+//     }
+//     sort(ans,ans+idx);
+//     for(int i=0;i<idx;i++){
+//         cout<<ans[i]<<" ";
+//     }
+//     // cout<<n<<m<<endl;
+//     cout<<endl;
+// }
+
+// // solution 2
+// vector<vector<int>>adj;
+// int n,m,idx,minCycleSum=200005;
+// vector<int>vis,stack,ans;
+
+// void detectCycle2(int node,int index){
+//     if(vis[node]){
+//         int sum=node;
+//         for(int i=index-2;i>=0 && stack[i]!=node;i--){
+//             sum+=stack[i];
+//         }
+//         if(sum<minCycleSum){
+//             idx=0;
+//             ans[idx++]=node;
+//             for(int i=index-2;i>=0 && stack[i]!=node;i--){
+//                 ans[idx++]=stack[i];
+//             }
+//         }
+//         return;
+//     }
+//     else{
+//         vis[node]=1;
+//         for(int num:adj[node]){
+//             stack[index]=num;
+//             detectCycle2(num,index+1);
+//         }
+//         vis[node]=0;
+//     }
+// }
+
+// void solve2(){   
+//     cin>>n>>m;
+//     adj.resize(n+1);
+//     vis.resize(n+1,0);
+//     stack.resize(n+1);
+//     ans.resize(n+1);
+//     for(int i=0;i<m;i++){
+//         int u,v; cin>>u>>v;
+//         adj[u].pb(v);
+//     }
+//     for(int i=1;i<=n;i++){
+//         stack[0]=i;
+//         detectCycle2(i,1);
+//     }
+//     sort(ans.begin(),ans.begin()+idx);
+//     for(int i=0;i<idx;i++){
+//         cout<<ans[i]<<" ";
+//     }
+//     // cout<<n<<m<<endl;
+//     cout<<endl;
+// }
+
+int n,m,min_sum;
+vector<vector<int>>adj;
+vector<int>ans;
+
+void findWay(int idx,int mask){
+    // cout<<idx<<" "<<mask<<" "<<(mask & (1<<idx))<<endl;
+    if((mask & (1<<idx))!=0){
+        // loop created
+        int sum=0;
+        vector<int>temp;
+        for(int i=0;i<n;i++){
+            if((mask & (1<<i))!=0) sum+=(i+1),temp.push_back(i+1);
+        }
+        if(sum<min_sum){
+            min_sum=sum;
+            ans=temp;
+        }
+        // cout<<"Found"<<endl;
+        return;
+    }
+    for(int i=0;i<int(adj[idx].size());i++){
+        findWay(adj[idx][i],(mask | (1<<idx)));
+    }                                                         
+}
+
+void solve3() {
+    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
+    cin>>n>>m;
+    adj.resize(n);
+    for(int i=0;i<m;i++){
+        int u,v; cin>>u>>v;
+        u--,v--;
+        adj[u].push_back(v);
+    }
+    min_sum=1e9;
+    for(int i=0;i<n;i++){
+        findWay(i,0);
+    }
+    sort(ans.begin(),ans.end());
+    // cout<<min_sum<<endl;
+    for(int i=0;i<int(ans.size());i++){
+        cout<<ans[i]<<" ";
+    }
+    cout<<endl;
+}
+
+int main() {
+    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
+    // solve1();
+    // solve2();
+    solve3();
+    return 0;
+}

2. Kim and Refrigerators/5.cpp

@@ -0,0 +1,58 @@
+// Solution with Bitmasking
+#include <cmath>
+#include <cstdio>
+#include <vector>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+
+int n; 
+int startX,startY,endX,endY;
+int ans;
+vector<pair<int,int>>v;
+int allone;
+
+int dist(int x1,int y1,int x2,int y2){
+    return abs(x1-x2)+abs(y1-y2);
+}
+
+void find(int sum,int mask,int last){
+    if(mask==allone){
+        int d=dist(v[last].first,v[last].second,endX,endY);
+        ans=min(ans,sum+d);
+        return;
+    }
+    for(int i=0;i<n;i++){
+        if((mask & (1<<i))==0){
+            int d=dist(v[last].first,v[last].second,v[i].first,v[i].second);
+            find(sum+d,(mask | (1<<i)),i);
+        }
+    }
+}
+
+void solve(){
+    cin>>n;
+    cin>>startX>>startY>>endX>>endY;
+    v.clear();
+    for(int i=0;i<n;i++){
+        int x,y; cin>>x>>y;
+        v.push_back({x,y});
+    }
+    ans=1e9;
+    allone=(1<<n)-1;
+    for(int i=0;i<n;i++){
+        int sum=dist(startX,startY,v[i].first,v[i].second);
+        find(sum,(1<<i),i);
+    }
+    cout<<ans<<endl;
+}
+
+int main() {
+    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
+    int T=10;
+    for(int t=1;t<=T;t++){
+        cout<<"# "<<t<<" ";
+        solve();
+    }
+    return 0;
+}