68 lines
1.6 KiB
Java
68 lines
1.6 KiB
Java
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import java.util.*;
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import java.util.function.*;
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public class BinarySearch {
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// 000[1]11
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// warning: overflows in lines 1-4
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public static int binarySearchFirstTrueSimple(IntPredicate predicate, int fromInclusive, int toInclusive) {
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int lo = fromInclusive - 1;
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int hi = toInclusive + 1;
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while (hi - lo > 1) {
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int mid = (lo + hi) / 2;
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if (!predicate.test(mid)) {
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lo = mid;
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} else {
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hi = mid;
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}
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}
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return hi;
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}
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// 000[1]11
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// correct binary search
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public static int binarySearchFirstTrue(IntPredicate predicate, int fromInclusive, int toExclusive) {
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int lo = fromInclusive;
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int hi = toExclusive;
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while (lo < hi) {
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// int mid = lo + ((hi - lo) >>> 1);
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int mid = (lo & hi) + ((lo ^ hi) >> 1);
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if (!predicate.test(mid)) {
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lo = mid + 1;
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} else {
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hi = mid;
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}
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}
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return hi;
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}
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public static double binarySearch(DoublePredicate predicate, double lo, double hi) {
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for (int step = 0; step < 1000; step++) {
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double mid = (lo + hi) / 2;
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if (!predicate.test(mid)) {
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lo = mid;
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} else {
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hi = mid;
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}
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}
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return hi;
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}
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// random test
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public static void main(String[] args) {
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Random rnd = new Random(1);
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for (int step = 0; step < 100_000; step++) {
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int n = rnd.nextInt(20);
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boolean[] b = new boolean[n];
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int firstTrue = rnd.nextInt(n + 1);
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Arrays.fill(b, firstTrue, n, true);
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int res1 = binarySearchFirstTrueSimple(i -> b[i], 0, n - 1);
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int res2 = binarySearchFirstTrue(i -> b[i], 0, n);
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if (res1 != firstTrue || res1 != res2)
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throw new RuntimeException();
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}
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System.out.println(Math.sqrt(2) == binarySearch(x -> x * x >= 2, 0, 2));
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}
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}
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