47 lines
1019 B
Java
47 lines
1019 B
Java
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package Maths;
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public class BinaryPow {
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/**
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* Calculate a^p using binary exponentiation
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* [Binary-Exponentiation](https://cp-algorithms.com/algebra/binary-exp.html)
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*
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* @param a the base for exponentiation
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* @param p the exponent - must be greater than 0
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* @return a^p
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*/
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public static int binPow(int a, int p) {
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int res = 1;
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while (p > 0) {
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if ((p & 1) == 1) {
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res = res * a;
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}
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a = a * a;
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p >>>= 1;
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}
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return res;
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}
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/**
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* Function for testing binary exponentiation
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* @param a the base
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* @param p the exponent
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*/
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public static void test(int a, int p) {
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int res = binPow(a, p);
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assert res == (int) Math.pow(a, p) : "Incorrect Implementation";
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System.out.println(a + "^" + p + ": " + res);
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}
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/** Main Function to call tests
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*
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* @param args System Line Arguments
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*/
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public static void main(String[] args) {
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// prints 2^15: 32768
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test(2, 15);
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// prints 3^9: 19683
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test(3,9);
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}
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}
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