Updated repo with new codes LC-STL

Author: Arun-Kumar-Rathod

C++/STL C++/STL_LEC_1_Array_1.cpp

@@ -0,0 +1,47 @@
+/*  if we declare an array and don't initialize values then in int main it will have garbage values 
+where if we declare them in global space it will be initialized to zeroes  */
+
+/*  If we initialize the first element with any number other numbers in the array will be zeroes  */
+
+#include<bits/stdc++.h>
+using namespace std;
+
+array<int, 10> arr;
+
+int main(){
+    array<int, 10> arr_1;
+
+    // Printing the global array
+    for(int i=0; i<10; i++){
+        cout<< arr[i] << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // 0 0 0 0 0 0 0 0 0 0 
+
+    // Printing the local array
+    for(int i=0; i<10; i++){
+        cout<< arr_1[i] << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // -1663042624 98 2095127112 32759 -802929584 559 -1663042384 1 213850828 142645788 
+
+    // Printing a local array where we intialize half array & leave other half
+    array<int, 10> arr_2 = {1,2,3};
+    for(int i=0; i<10; i++){
+        cout<< arr_2[i] << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // 1 2 3 0 0 0 0 0 0 0
+
+    // Proving that initialzing the first element with any value makes all the values of the array zero
+    array<int, 10> arr_3 = {0};
+    for(int i=0; i<10; i++){
+        cout<< arr_3[i] << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // 0 0 0 0 0 0 0 0 0 0
+}

C++/STL C++/STL_LEC_1_Array_2.cpp

@@ -0,0 +1,34 @@
+/* 
+array.fill method
+<ArrayName>.fill(<value>)
+
+Accessing elements using at
+<ArrayName>.at(<index>)
+*/ 
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    array<int, 10> arr;
+
+    // Before filling the array
+    for(int i=0; i<10; i++){
+        cout<< arr[i] << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // 450756608 32758 0 2 782236016 23 450763352 32758 -1731603232 527 
+
+    // Fill Method
+    arr.fill(5);
+
+    // After filling
+    // Accessing elements using .at()
+    for(int i=0; i<10; i++){
+        cout<< arr.at(i) << " ";
+    }
+    cout<<"\n";
+    // Output:
+    // 5 5 5 5 5 5 5 5 5 5
+}

C++/STL C++/STL_LEC_1_Iterators_1.cpp

@@ -0,0 +1,35 @@
+/* 
+Iterators:
+begin() -> points to the first element of the array
+end() -> points after the last element of the array
+rbegin() -> points to the last element of the array
+rend() -> points before  first element of the array
+*/ 
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    array<int, 5> arr = { 1, 3, 4, 5, 6};
+    for(auto it = arr.begin(); it!=arr.end(); it++){
+        cout << *it << " ";
+    } cout << endl;
+
+    for(auto it = arr.rbegin(); it!=arr.rend(); it++){
+        cout << *it << " ";
+    } cout<<endl;
+
+    // also called for-each loop
+    for(auto it: arr){
+        cout << it << " ";
+    } cout << endl;
+
+    string s = "arunkumar";
+    for(auto c: s){
+        cout << c << " ";
+    } cout << endl;
+
+    cout << arr.size() << endl;
+    cout << arr.front() << " " << arr.at(0) << endl;
+    cout << arr.back() << " " << arr.at(arr.size()-1) << endl;
+}

C++/STL C++/STL_LEC_1_vector_1.cpp

@@ -0,0 +1,36 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    // vector<int> arr;
+    // arr.push_back(0);
+    // arr.push_back(2);
+    // cout << arr.size() << endl; // 2
+    // arr.pop_back(); // element 2 got removed
+    // cout << arr.size() << endl; // 1
+    // arr.push_back(1); arr.push_back(5); arr.push_back(3); arr.push_back(4);
+    // cout << arr.size() << endl; // 5
+
+    // // clear will delete all vector elements but will not delete the vector
+    // arr.clear();
+    // cout << arr.size() << endl; // 0
+
+    // what if we want to create an vector of size x
+    // vector<int> ar(4,0); // {0 0 0 0} here 4 is the size and the following is the element with which the vector needs to initialized
+    // vector<int> ar1(10,5); // {5 5 5 5 5 5 5 5 5 5} size 10 intialize all elements with 5
+
+    // copying a vector into another
+    // vector<int> ar2(ar1); // {5 5 5 5 5 5 5 5 5 5}
+    // vector<int> ar3 = {1,2,3,4,5,6};
+    // vector<int> ar4(ar3.begin(), ar3.begin()+2); // {1,2} 2nd element is not inclusive [)
+
+    // emplace_back is faster than push_back
+    vector<int> ar5; 
+    ar5.emplace_back(5);
+    ar5.emplace_back(2);
+    ar5.emplace_back(8);
+    for(auto it=ar5.begin(); it != ar5.end(); it++){
+        cout << *it << " ";
+    }
+
+}

C++/STL C++/STL_LEC_1_vector_2.cpp

@@ -0,0 +1,38 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    // 2d array
+    vector<vector<int>> arr;
+
+    vector<int> ar1;
+    ar1.emplace_back(1);
+    ar1.emplace_back(2);
+    ar1.emplace_back(3);
+
+    vector<int> ar2;
+    ar2.emplace_back(4);
+    ar2.emplace_back(5);
+    ar2.emplace_back(6);
+
+    vector<int> ar3;
+    ar3.emplace_back(7);
+    ar3.emplace_back(8);
+    ar3.emplace_back(9);
+
+    arr.push_back(ar1);
+    arr.push_back(ar2);
+    arr.push_back(ar3);
+
+    for(auto vectr: arr){
+        for(auto it: vectr){
+            cout << it << " ";
+        } cout << endl;
+    }
+
+    // 2D vector 10x20
+    vector<vector<int>> vec2d(10, vector<int> (20,0));
+
+    // 3D vector 10x20x30
+    vector<vector<vector<int>>> vec3d(10, vector<vector<int>> (20, vector<int> (30, 0)));
+}

C++/STL C++/STL_LEC_2_Map_1.cpp

@@ -0,0 +1,29 @@
+// a map stores the values in key value pairs and orders them according to keys(alphabetically for example)
+// a unordered map stores values but are not ordered and keys are unique here
+// a multipmap is ordered and storing multiple duplicate keys is possible
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    map<string,int> mpp;
+    mpp["arun"] = 17;
+    mpp["sam"] = 25;
+    mpp["gilly"] = 21;
+    mpp["jon"] = 1;
+    mpp["gilly"] = 21; 
+
+    cout << "size: " << mpp.size() << endl; // 4
+    cout << "Map is empty: " << mpp.empty() << endl;
+
+    mpp.erase(mpp.find("sam"));
+    for(auto it: mpp){
+        cout << it.first << " " << it.second << endl;
+    }
+
+    // unordered map
+    unordered_map<string, int> ump;
+    //all functions more or less similar to map
+
+    multimap<string,int> mmp;
+    //all functions more or less similar to map
+}

C++/STL C++/STL_LEC_2_PriorityQueue_1.cpp

@@ -0,0 +1,19 @@
+// PQ stores elements in descending order
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    cout << "Max PQ" << endl;
+    priority_queue<int> pq;
+    pq.push(1); pq.push(3); pq.push(8); pq.push(12);
+    cout << pq.top() << endl; // 12
+    pq.pop();
+    cout << pq.top() << endl; // 8
+
+    cout << endl << "Min PQ" << endl;
+    priority_queue<int,vector<int>,greater<int>> pq1;
+    pq1.push(1); pq1.push(3); pq1.push(8); pq1.push(12);
+    cout << pq1.top() << endl; // 1
+    pq1.pop();
+    cout << pq1.top() << endl; // 3
+}

C++/STL C++/STL_LEC_2_Questions_1.cpp

@@ -0,0 +1,25 @@
+// given N elements, print the elements that occurs maximum no . of times
+// input
+// 5
+// 1 3 3 3 2
+
+// output
+// 3
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    int n, max=1;
+    map<int,int> mpp;
+    cin >> n;
+    while(--n){
+        int x;
+        cin >> x;
+        mpp[x]++;
+        if(mpp[x] > mpp[max]){
+            max = x;
+        }
+    }
+    cout << "The Number with highest frequency is: " << mpp[max];
+}

C++/STL C++/STL_LEC_2_Questions_2.cpp

@@ -0,0 +1,24 @@
+// given N elements, print all the elements in sorted order
+// input
+// 6
+// 6 6 3 2 3 5
+
+// output
+// 2 3 3 5 6 6
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    int n;
+    multiset<int> ms;
+    cin >> n;
+    while(n--){
+        int x;
+        cin >> x;
+        ms.insert(x);
+    }
+    for(auto it: ms){
+        cout << it << " ";
+    }
+}

C++/STL C++/STL_LEC_2_Set_1.cpp

@@ -0,0 +1,70 @@
+// A set has only unique elements 
+// The first element is the smallest and the 2nd element is the 2nd smallest element (continued trend)
+// an unordered set has elements in random order (No ascending) and elements are still unique here
+// In a multiset the elements are stored in ascending fashion and we can have multiple instances of a same element
+
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    // set<int> st;
+
+    // int n,x=0;
+    // cin >> n;
+    // for(int i=0; i<n; i++){
+    //     cin >> x;
+    //     st.insert(x);
+    // }
+    
+    // st.erase(st.begin()); // will remove the first element in the set (the smallesto one)
+    // st.erase(5); // will remove the element specified
+
+    // new code below
+
+    // set<int> st1 = {5,2,1,4,3}; // the order doesnt matter it will be in ascending only
+    // auto it1 = st1.find(2);
+    // for(auto it=st1.begin(); it!= st1.end(); it++){
+    //     cout << *it << " ";
+    // }
+    // cout << "\nsize of the set before erase: " << st1.size() << endl;
+    // st1.erase(it1); // iterator pointing to the element specified
+    
+    // for(auto it=st1.begin(); it!= st1.end(); it++){
+    //     cout << *it << " ";
+    // }
+    // cout << endl << "size of the set after erase: " << st1.size() << endl;
+
+    //new code below
+    // set<int> st2 = {5,2,1,4,3};
+    // for(auto it: st2){
+    //     cout << it << " ";
+    // }
+
+    // unordered set
+    // unordered_set<int> ust;
+    // unordered_set<int> ust1 = {9,4,1}; // 9 4 1
+    // ust.emplace(5); // 5
+    // ust.insert(21); // 5 21
+    // ust.emplace(9); // 5 21 9
+
+    // ust.erase(21); // 9 5
+    // ust1.erase(ust1.find(9)); // 4 1
+    // for(auto it: ust1){
+    //     cout << it << " ";
+    // }
+
+    // Multiset
+    multiset<int> ms;
+    ms.insert(8);
+    ms.emplace(6);
+    ms.insert(6);
+    ms.emplace(5); // 5 6 6 8
+
+    ms.size(); // 4
+
+    ms.erase(ms.begin()); // 6 6 8
+    ms.erase(ms.find(6)); // 6 8
+
+    ms.size(); // 2
+}