Solved the medium Section problems of algos/range_qeries/prefix sum

algos/range_queries/PrefixSum/soln/Sujal/b_reverse_sort.cpp

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+//PROBLEM STATEMENT- https://codeforces.com/problemset/problem/1605/B
+
+//SUBMISSION LINK- https://codeforces.com/problemset/submission/1605/356028420
+
+//APPROACH- For every gap, check the ones on left and zeroes on right using prefix and suffix sums
+//          if at any point, they are equal(and non zero), they can be swapped
+//TIME COMPLEXITY- O(n*n)
+//SPACE COMPLEXITY- O(n*n)
+
+
+
+
+#include<bits/stdc++.h>
+using namespace std;
+
+void solve(){
+    int n;cin>>n;
+    string s;cin>>s;
+    if(n==1){cout<<0<<"\n";return;}
+
+    vector<vector<int>> L(n-1),R(n-1);
+
+    if(s[0]=='1')L[0].push_back(0);
+    for(int i=1;i<n-1;i++){
+        L[i]=L[i-1];
+        if(s[i]=='1')L[i].push_back(i);
+    }
+
+    if(s[n-1]=='0')R[n-2].push_back(n-1);
+    for(int i=n-2;i>0;i--){
+        R[i-1]=R[i];
+        if(s[i]=='0')R[i-1].push_back(i);
+    }
+
+    for(int i=0;i<n-1;i++){
+        int a=L[i].size(),b=R[i].size();
+        if(a==b&&a){
+            cout<<1<<"\n"<<a+b<<" ";
+            for(int x:L[i])cout<<x+1<<" ";
+            for(auto it=R[i].rbegin();it!=R[i].rend();it++)cout<<*it+1<<" ";
+            cout<<"\n";
+            return;
+        }
+    }
+    cout<<0<<"\n";
+}
+
+int main(){
+    int t;cin>>t;
+    while(t--)solve();
+}

algos/range_queries/PrefixSum/soln/Sujal/tracking_segments.cpp

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+//PROBLEM STATEMENT- https://codeforces.com/problemset/problem/1843/E
+
+//SUBMISSION LINK- https://codeforces.com/problemset/submission/1843/356028549
+
+
+//APPROACH- Standard binary search on queries as they are monotonues (F F F T T TT)
+//TIME COMPLEXITY- O(nlogn)
+//SPACE COMPLEXITY- O(n)
+
+
+
+
+#include<bits/stdc++.h>
+using namespace std;
+
+bool ok(vector<pair<int,int>>&seg,vector<int>&q,int mid,int n){
+    vector<int>a(n,0);
+    for(int i=0;i<mid;i++)a[q[i]-1]=1;
+
+    vector<int>pre(n+1,0);
+    for(int i=0;i<n;i++)pre[i+1]=pre[i]+a[i];
+
+    for(auto &p:seg){
+        if(pre[p.second]-pre[p.first-1]>(p.second-p.first+1)/2)
+            return true;
+    }
+    return false;
+}
+
+void solve(){
+    int n,m;cin>>n>>m;
+    vector<pair<int,int>>seg(m);
+    for(int i=0;i<m;i++)cin>>seg[i].first>>seg[i].second;
+
+    int qn;cin>>qn;
+    vector<int>q(qn);
+    for(int i=0;i<qn;i++)cin>>q[i];
+
+    int l=1,r=qn,ans=-1;
+    while(l<=r){
+        int mid=(l+r)/2;
+        if(ok(seg,q,mid,n)){
+            ans=mid;
+            r=mid-1;
+        }else l=mid+1;
+    }
+    cout<<ans<<"\n";
+}
+
+int main(){
+    int t;cin>>t;
+    while(t--)solve();
+}