Building Abstractions with Functions - Functions and the Processes They Generate - Exponentiation - iterative exponentiation process, successive squaring
Structure and Interpretation of Computer Programs: JavaScript Edition(Harold Abelson(著)、Gerald Jay Sussman(著)、Julie Sussman(著)、The MIT Press)のChapter 1(Building Abstractions with Functions)、1.2(Functions and the Processes They Generate)、1.2.4(Exponentiation)、Exercise 1.16の解答を求めてみる。
コード
function square(x) {
return x * x;
}
function is_even(n) {
return n % 2 === 0;
}
function expt(b, n) {
function iter(n, a) {
return n === 0 ?
a :
is_even(n) ?
iter(n - 2, square(b) * a) :
iter(n - 1, b * a);
}
return iter(n, 1);
}
console.log(expt(2, 0));
console.log(expt(2, 1));
console.log(expt(2, 2));
console.log(expt(2, 10));
console.log(expt(2, 11));
console.log(expt(2, 100));
入出力結果(Terminal, Zsh)
% node answer1.16.js
1
2
4
1024
2048
1.2676506002282294e+30
%