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Matrix/common.cpp

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+/*
+Common elements in all rows of a given matrix
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+void commonElements(int a[10][10], int n, int m)
+{
+    unordered_map<int, int> mp;
+    for (int i = 0; i < m; i++) //initializing first row elements with value 1
+    {
+        mp[a[0][i]] = 1;
+    }
+    for (int i = 1; i < n; i++) //checking from second row
+    {
+        for (int j = 0; j < m; j++)
+        {
+            if (mp[a[i][j]] == i) //if element is present in map
+            {
+                mp[a[i][j]] = i + 1;                 //count increasing by 1
+                if (i == n - 1 and mp[a[i][j]] == n) //if last row
+                {
+                    cout << a[i][j] << " ";
+                }
+            }
+        }
+    }
+}
+
+int main()
+{
+
+    int a[10][10], i, j, n, m;
+
+    cout << "Enter number of rows  (between 1 and 10): ";
+    cin >> n;
+    cout << "Enter number of columns  (between 1 and 10): ";
+    cin >> m;
+
+    cout << endl
+         << "Enter elements of the matrix: " << endl;
+
+    // Storing elements of first matrix entered by user.
+    for (i = 0; i < n; ++i)
+    {
+        for (j = 0; j < m; ++j)
+        {
+            cout << "Enter element a" << i + 1 << j + 1 << " : ";
+            cin >> a[i][j];
+        }
+    }
+    commonElements(a, n, m);
+
+    return 0;
+}

Matrix/kMat.cpp

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+/*
+Kth element in Matrix 
+Given a N x N matrix, where every row and column is sorted in non-decreasing order.
+ Find the kth smallest element in the matrix.
+
+Example 1:
+Input:
+N = 4
+mat[][] =     {{16, 28, 60, 64},
+                   {22, 41, 63, 91},
+                   {27, 50, 87, 93},
+                   {36, 78, 87, 94 }}
+K = 3
+Output: 27
+Explanation: 27 is the 3rd smallest element.
+ 
+
+Example 2:
+Input:
+N = 4
+mat[][] =     {{10, 20, 30, 40}
+                   {15, 25, 35, 45}
+                   {24, 29, 37, 48}
+                   {32, 33, 39, 50}}
+K = 7
+Output: 30
+Explanation: 30 is the 7th smallest element.
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+int count(int a[10][10], int n, int m, int mid)
+{
+    int count = 0; //to store count of values smaller or equal to mid
+    int j = m - 1; //from reverse
+    for (int i = 0; i < n; i++)
+    {
+        for (j; j >= 0; j--)
+        {
+            if (a[i][j] <= mid)
+            {
+                count += j + 1;
+                //no of columns +1 (col no. starts from 0)
+                break;
+            }
+        }
+    }
+    return count;
+}
+
+int kSmall(int a[10][10], int n, int m, int k)
+{
+
+    int low = a[0][0];
+    int high = a[n - 1][m - 1];
+    while (low < high)
+    {
+        int mid = floor((high - low) / 2 + 1);
+        int c = count(a, n, m, mid);
+        if (c >= k)
+        {
+            high = mid;
+        }
+        else
+        {
+            low = mid + 1;
+        }
+    }
+
+    return low;
+}
+
+int main()
+{
+    int a[10][10], i, j, n, m, k;
+
+    cout << "Enter number of rows  (between 1 and 10): ";
+    cin >> n;
+    cout << "Enter number of columns  (between 1 and 10): ";
+    cin >> m;
+
+    cout << endl
+         << "Enter elements of the matrix: " << endl;
+
+    // Storing elements of first matrix entered by user.
+    for (i = 0; i < n; ++i)
+    {
+        for (j = 0; j < m; ++j)
+        {
+            cout << "Enter element a" << i + 1 << j + 1 << " : ";
+            cin >> a[i][j];
+        }
+    }
+
+    cout << "Enter value of k (kth smallest element): ";
+    cin >> k;
+
+    int ans = kSmall(a, n, m, k);
+    cout << ans << endl;
+    return 0;
+}