Arrays: Static, Dynamic & Multi-dimensional

8. Practice Problems

Try each problem first, then click Show Answer to compare with a runnable solution.

1. Find the maximum subarray sum using the naive O(n²) approach.
   Naive O(n²) পদ্ধতিতে maximum subarray sum বের করুন।
   ✨ Show Answer (উত্তর দেখুন)

   ans1.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<int> a = {-2,1,-3,4,-1,2,1,-5,4};
       int n = a.size(), best = INT_MIN;
       for (int i = 0; i < n; i++) {
           int s = 0;
           for (int j = i; j < n; j++) { s += a[j]; best = max(best, s); }
       }
       cout << best << "\n";
   }

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2. Reverse an array in-place using two pointers.
   Two-pointer পদ্ধতিতে in-place একটি array reverse করুন।
   ✨ Show Answer (উত্তর দেখুন)

   ans2.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<int> a = {1,2,3,4,5};
       int l = 0, r = a.size() - 1;
       while (l < r) swap(a[l++], a[r--]);
       for (int x : a) cout << x << " ";
       cout << "\n";
   }

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3. Rotate an array right by k positions in O(n) time and O(1) space.
   O(n) সময় ও O(1) space-এ array-কে ডানে k বার rotate করুন।
   ✨ Show Answer (উত্তর দেখুন)

   ans3.cpp

   #include <bits/stdc++.h>
   using namespace std;
   void rev(vector<int>& a,int l,int r){while(l<r) swap(a[l++],a[r--]);}
   int main() {
       vector<int> a = {1,2,3,4,5,6,7};
       int n = a.size(), k = 3 % n;
       rev(a,0,n-1); rev(a,0,k-1); rev(a,k,n-1);
       for (int x : a) cout << x << " ";
       cout << "\n";
   }

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4. Print a 2D matrix in spiral order.
   2D matrix-কে spiral order-এ print করুন।
   ✨ Show Answer (উত্তর দেখুন)

   ans4.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<vector<int>> m = {{1,2,3},{4,5,6},{7,8,9}};
       int top=0, bot=m.size()-1, lt=0, rt=m[0].size()-1;
       while (top <= bot && lt <= rt) {
           for (int j=lt;j<=rt;j++) cout << m[top][j] << " "; top++;
           for (int i=top;i<=bot;i++) cout << m[i][rt] << " "; rt--;
           if (top <= bot) { for (int j=rt;j>=lt;j--) cout << m[bot][j] << " "; bot--; }
           if (lt <= rt)  { for (int i=bot;i>=top;i--) cout << m[i][lt] << " "; lt++; }
       }
       cout << "\n";
   }

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5. Find the second largest element in a single pass.
   Array-এ একবার ঘুরেই দ্বিতীয় সর্বোচ্চ element বের করুন।
   ✨ Show Answer (উত্তর দেখুন)

   ans5.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<int> a = {12,35,1,10,34,35,1};
       int first = INT_MIN, second = INT_MIN;
       for (int x : a) {
           if (x > first) { second = first; first = x; }
           else if (x > second && x < first) second = x;
       }
       cout << second << "\n";
   }

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6. Move all zeros to the end of the array, preserving order of non-zeros, in O(n).
   Array-এর সব 0-কে শেষে সরান (non-zero-দের আপেক্ষিক order বজায় রেখে), O(n)-এ।
   ✨ Show Answer (উত্তর দেখুন)

   ans6.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<int> a = {0,1,0,3,12};
       int j = 0;
       for (int i = 0; i < (int)a.size(); i++)
           if (a[i] != 0) swap(a[i], a[j++]);
       for (int x : a) cout << x << " ";
       cout << "\n";
   }

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7. Given two sorted arrays, merge them into a single sorted array.
   দুটি sorted array-কে merge করে একটি sorted array বানান।
   ✨ Show Answer (উত্তর দেখুন)

   ans7.cpp

   #include <bits/stdc++.h>
   using namespace std;
   int main() {
       vector<int> a = {1,3,5,7}, b = {2,4,6,8,10};
       vector<int> c;
       int i=0, j=0;
       while (i < (int)a.size() && j < (int)b.size()) {
           if (a[i] <= b[j]) c.push_back(a[i++]);
           else c.push_back(b[j++]);
       }
       while (i < (int)a.size()) c.push_back(a[i++]);
       while (j < (int)b.size()) c.push_back(b[j++]);
       for (int x : c) cout << x << " ";
       cout << "\n";
   }

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