51 lines
992 B
JavaScript
51 lines
992 B
JavaScript
(function () {
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function memoizedHailstone() {
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var dctMemo = {};
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return function hailstone(n) {
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var value = dctMemo[n];
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if (typeof value === "undefined") {
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dctMemo[n] = value = (n === 1) ?
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[1] : ([n].concat(hailstone(n % 2 ? n * 3 + 1 : n / 2)));
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}
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return value;
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}
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}
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// Derived a memoized version of the function,
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// which can reuse previously calculated paths
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var fnCollatz = memoizedHailstone();
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// Iterative version of range
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// [m..n]
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function range(m, n) {
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var a = Array(n - m + 1),
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i = n + 1;
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while (i--) a[i - 1] = i;
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return a;
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}
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// Fold/reduce over an array to find the maximum length
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function longestBelow(n) {
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return range(1, n).reduce(
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function (a, x, i) {
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var lng = fnCollatz(x).length;
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return lng > a.l ? {
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n: i + 1,
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l: lng
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} : a
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}, {
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n: 0,
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l: 0
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}
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)
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}
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return longestBelow(100000);
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})();
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