added code

Author: Prateek Narang

.DS_Store

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+#include<iostream>
+#include<vector>
+using namespace std;
+
+int main(){
+	//Demo Vector
+	//vector<int> arr =  //{1,2,10,12,15};
+
+	//Fill Constructor
+	vector<int> arr(10,7);
+
+	//Fill Constructor
+	vector<int> visited(100,0);
+
+	//Pop_back
+	arr.pop_back();
+	// Push_Back O(1)
+	arr.push_back(16);
+
+	//Print all the elements
+	for(int x : arr){
+		cout << x <<",";
+	}
+
+	/*for(int i=0;i< arr.size(); i++){
+		cout << arr[i] <<endl;
+	}*/
+
+	return 0;
+}

01 Arrays & Vectors/.DS_Store

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+#include<iostream>
+#include<vector>
+using namespace std;
+
+
+int main(){
+	//2D Vector 
+	vector< vector<int> > arr =  {
+		{1,2,3},
+		{4,5,6},
+		{7,8,9,10},
+		{11,12}};
+
+
+	arr[0][0] += 10; //update
+
+	for(int i=0;i< arr.size(); i++){
+
+		for(int number : arr[i]){
+			cout << number <<",";
+		}
+		cout <<endl;
+	}
+	
+
+	return 0;
+}

01 Arrays & Vectors/01 vector.cpp

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+#include<iostream>
+#include<vector>
+#include<algorithm>
+using namespace std;
+
+vector<vector<int> > triplets(vector<int> arr,int targetSum){
+	//Logic 
+	int n = arr.size();
+	sort(arr.begin(),arr.end());
+	vector<vector<int> > result;
+
+	// Pick every a[i], pair sum for remaining part
+	for(int i=0; i<=n-3;i++){
+
+		int j = i + 1;
+		int k = n - 1;
+
+		//two pointer approach
+		while(j < k){
+			int current_sum = arr[i];
+			current_sum += arr[j];
+			current_sum += arr[k];
+
+			if(current_sum==targetSum){
+				result.push_back({arr[i],arr[j],arr[k]});
+				j++;
+				k--;
+			}
+			else if(current_sum > targetSum){
+				k--;
+			}
+			else{
+				j++;
+			}
+		}
+
+	}
+	return result;
+
+}
+
+int main(){
+
+	vector<int> arr{1, 2, 3, 4, 5, 6, 7, 8, 9, 15};
+	int S = 18;
+
+	auto result = triplets(arr,S);
+
+	for(auto v : result){
+		for(auto no : v){
+			cout<<no<<",";
+		}
+		cout<<endl;
+	}
+
+
+	return 0;
+}

01 Arrays & Vectors/02 2dvector.cpp

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+#include<iostream>
+#include<vector>
+using namespace std;
+
+
+int highest_mountain(vector<int> a){
+	int n = a.size();
+
+	int largest = 0;
+
+	for(int i=1;i<=n-2;){
+
+		//check a[i] is peak or not
+		if(a[i]>a[i-1] and a[i]>a[i+1]){
+			//do some work
+			int cnt = 1;
+			int j = i;
+			//cnt backwards (left)
+			while(j>=1 and a[j]>a[j-1]){
+				j--;
+				cnt++;
+			}
+			//cnt forwards (right)
+			while(i<=n-2 and a[i]>a[i+1]){
+				i++;
+				cnt++;
+			}
+			largest = max(largest,cnt);
+
+		}
+		else{
+			i++;
+		}
+	}
+	return largest;
+
+}
+
+int main(){
+
+	vector<int> arr{5,6,1,2,3,4,5,4,3,2,0,1,2,3,-2,4};
+
+	cout<< highest_mountain(arr)<<endl;
+
+
+
+	return 0;
+}

01 Arrays & Vectors/04 triplets.cpp

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+#include<iostream>
+#include<vector>
+#include<unordered_set>
+using namespace std;
+
+int largestBand(vector<int> arr){
+	int n = arr.size();
+	unordered_set<int> s;
+	
+	//Data inside a set
+	for(int x : arr){
+		s.insert(x);
+	}
+
+	//Iterate over the arr
+	int largestLen = 1;
+
+	for(auto element : s){
+		int parent = element - 1;
+
+		if(s.find(parent)==s.end()){
+			//find entire band / chain starting from element
+			int next_no = element + 1;
+			int cnt = 1;
+
+			while(s.find(next_no)!=s.end()){
+				next_no++;
+				cnt++;
+			}
+
+			if(cnt>largestLen){
+				largestLen = cnt;
+			}
+		}
+	}
+
+
+	return largestLen;
+}
+
+
+
+int main(){
+
+	vector<int> arr{1, 9, 3, 0, 18, 5, 2, 10, 7, 12, 6};
+	cout << largestBand(arr)<<endl;
+
+	return 0;
+}

01 Arrays & Vectors/05 mountain.cpp

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+#include <iostream>
+#include <vector>
+using namespace std;
+
+
+int trappedWater(vector<int> heights) {
+
+ 	//Complete
+ 	int n = heights.size();
+ 	if(n<=2){
+ 		return 0;
+ 	}
+
+ 	//Left Max, Right Max
+ 	vector<int> left(n,0), right(n,0);
+ 	left[0] = heights[0];
+ 	right[n-1] = heights[n-1];
+
+ 	for(int i=1;i<n;i++){
+ 		left[i] = max(left[i-1],heights[i]);
+ 		right[n-i-1] = max(right[n-i],heights[n-i-1]);
+ 	}
+
+ 	//water 
+ 	int water = 0;
+ 	for(int i=0;i<n;i++){
+ 		water += min(left[i],right[i]) - heights[i];
+ 	}
+	
+  return water;
+}
+
+int main() {
+    vector<int> water = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout<<trappedWater(water)<<endl;
+    return 0;
+}

01 Arrays & Vectors/06 longest_band.cpp

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+#include <iostream>
+#include<algorithm>
+#include <vector>
+using namespace std;
+
+bool outOfOrder(vector<int> arr,int i){
+	int x = arr[i];
+	if(i==0){
+		return x > arr[1];
+	}
+	if(i==arr.size()-1){
+		return x < arr[i-1];
+	}
+	return x > arr[i+1] or x < arr[i-1];
+
+}
+
+pair<int,int> subarraySort(vector<int> arr) {
+
+	int smallest = INT_MAX;
+	int largest = INT_MIN;
+
+	for(int i=0;i<arr.size();i++){
+		int x = arr[i];
+		
+		if(outOfOrder(arr,i)){
+			smallest = min(smallest,x);
+			largest = max(largest,x);
+		}
+	}
+
+	//next step find the right index where smallest and largest lie (subarray) for out solution
+	if(smallest==INT_MAX){
+		return {-1,-1};
+	}
+
+	int left = 0;
+	while(smallest >= arr[left]){
+		left++;
+	}
+	int right = arr.size() - 1;
+	while(largest <= arr[right]){
+		right--;
+	}
+
+	return {left,right};
+
+}
+
+int main() {
+    vector<int> arr = {1, 2, 3, 4, 5, 8, 6, 7, 9, 10, 11};
+    auto p = subarraySort(arr);
+    cout<< p.first <<" and "<<p.second <<endl;
+
+    return 0;
+}

01 Arrays & Vectors/07 rainwater-trap.cpp

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+#include <iostream>
+#include<vector>
+#include<algorithm>
+using namespace std;
+
+int countMinSwaps(vector<int> arr){
+
+    // Know the actual positions of elements (sorting)
+    //store the current indices
+    int n = arr.size();
+    pair<int,int> ap[n];
+    for(int i=0;i<n;i++){
+        ap[i].first = arr[i];
+        ap[i].second = i;
+    }
+
+    //sorting
+    sort(ap,ap+n);
+
+    //build the main logic
+    vector<bool> visited(n,false);
+
+    int ans = 0;
+    for(int i=0;i<n;i++){
+
+        // if element is visited or element is in right postion 
+        int old_position = ap[i].second;
+        if(visited[i]==true or old_position==i){
+            continue;
+        }
+
+        // visiting the element (index) for first time 
+        int node = i;
+        int cycle = 0;
+
+        while(!visited[node]){
+            visited[node] = true;
+            int next_node = ap[node].second;
+            node = next_node;
+            cycle += 1;
+        }
+        ans += (cycle-1);
+
+    }
+   
+    return ans;
+
+}
+
+
+int main() {
+    vector<int> arr{5,4,3,2,1};
+    cout<<countMinSwaps(arr)<<endl;
+    return 0;
+}