Create Anu has a Function Explanation.txt

Author: MathProgrammer

2020/Div 2/618 Div 2/Explanations/Anu has a Function Explanation.txt

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+Observation - f(x, y) will only have the bits that are set in x
+
+Every bit in y is subtracted so we cannot add any new bits to x, by performing f(x, y)
+
+-----
+
+This means that the value of a[1], represents the value of the entire function. 
+
+For every A[i], we will calculate the value of the function if we place A[i] at A[1]. 
+
+The answer will have all the bits set that are set only once in A[i] and not in any other array element. 
+
+If any bit is set in some other element A[j], it will get subtracted when we peform f(x, A[j])
+
+-----
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+int is_bit_set(long long n, int bit)
+{
+    return ((n & (1LL << bit)) != 0);
+}
+
+int main()
+{
+    int no_of_elements;
+    cin >> no_of_elements;
+    
+    vector <int> A(no_of_elements + 1);
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        cin >> A[i];
+    }
+    
+    const int NO_OF_BITS = 31;
+    vector <int> bit_frequency(NO_OF_BITS + 1, 0);
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        for(int b = 0; b <= NO_OF_BITS; b++)
+        {
+            if(is_bit_set(A[i], b))
+            {
+                bit_frequency[b]++;
+            }
+        }
+    }
+    
+    long long answer = 0;
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        long long answer_here = 0;
+        
+        for(int b = 0; b <= NO_OF_BITS; b++)
+        {
+            if(is_bit_set(A[i], b) && bit_frequency[b] == 1)
+            {
+                answer_here |= (1LL << b);
+            }
+        }
+        
+        if(answer_here > answer)
+        {
+            swap(A[i], A[1]);
+            
+            answer = answer_here;
+        }
+    }
+    
+    for(int i = 1; i <= no_of_elements; i++)
+    {
+        cout << A[i] << " ";
+    }
+    
+    cout << "\n";
+    return 0;
+}
+