interviews/training->training

puzzles/training/power_ap.cpp

@@ -0,0 +1,80 @@
+/*
+VIM: let b:lcppflags="-std=c++14 -O2 -pthread -I."
+VIM: let b:wcppflags="/O2 /EHsc /DWIN32"
+VIM-: let b:cppflags=g:Iboost.g:Itbb
+VIM-: let b:ldflags=g:Lboost.g:Ltbb
+VIM-: let b:ldlibpath=g:Bboost.g:Btbb
+VIM-: let b:argv=""
+*/
+#include <iostream>
+#include <exception>
+#include <chrono>
+#include <cmath>
+
+/*
+ * Given a positive integer which fits in a 32 bit signed integer, find if it
+ * can be expressed as A^P where P > 1 and A > 0. A and P both should be
+ * integers.
+ */
+
+bool isPower(int X) {
+
+    if ( X == 1 ){
+        return true;
+    }
+
+    double log_X = std::log(X);
+    long long end = log_X / std::log(2) +1;
+    for ( int i = 2; i <= end; ++i ) {
+        double A = std::exp(log_X/double(i));
+        double rA = std::round(A);
+        std::cout << "--> A=" << A << " r(" << rA <<  ") I=" << i << " diff=" << std::fabs(A-rA) << std::endl;
+        if ( std::fabs(A-rA) < 0.00001 ) {
+            int int_A = rA;
+            std::cout << "Testing --> A=" << A << " r("<<int_A <<  ") I=" << i << std::endl;
+            long long test = 1;
+            for ( int j = 0; j < i; ++j ) {
+                test *= int_A;
+            }
+            if ( test == X ) {
+                std::cout << "X=" << X << " A=" << int_A << " I=" << i << std::endl;
+                return true;
+            }
+        }
+    }
+    std::cout << "X=" << X << " no power found." << std::endl;
+    return false;
+}
+
+
+int main ( void )
+{try{
+    auto begin = std::chrono::high_resolution_clock::now();
+
+    isPower(1);
+    isPower(4);
+    isPower(3);
+    isPower(27);
+    isPower(1024000000);
+    isPower(1024*1024*1024);
+
+    //......
+
+    auto end = std::chrono::high_resolution_clock::now();
+    std::chrono::duration<double> seconds = end - begin;
+    std::cout << "Time: " << seconds.count() << std::endl;
+    return 0;
+}
+catch ( const std::exception& e )
+{
+    std::cerr << std::endl
+            << "std::exception(\"" << e.what() << "\")." << std::endl;
+    return 2;
+}
+catch ( ... )
+{
+    std::cerr  << std::endl
+            << "unknown exception." << std::endl;
+    return 1;
+}}
+