You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
68 lines
1.6 KiB
Java
68 lines
1.6 KiB
Java
import java.util.*;
|
|
import java.util.function.*;
|
|
|
|
public class BinarySearch {
|
|
|
|
// 000[1]11
|
|
// warning: overflows in lines 1-4
|
|
public static int binarySearchFirstTrueSimple(IntPredicate predicate, int fromInclusive, int toInclusive) {
|
|
int lo = fromInclusive - 1;
|
|
int hi = toInclusive + 1;
|
|
while (hi - lo > 1) {
|
|
int mid = (lo + hi) / 2;
|
|
if (!predicate.test(mid)) {
|
|
lo = mid;
|
|
} else {
|
|
hi = mid;
|
|
}
|
|
}
|
|
return hi;
|
|
}
|
|
|
|
// 000[1]11
|
|
// correct binary search
|
|
public static int binarySearchFirstTrue(IntPredicate predicate, int fromInclusive, int toExclusive) {
|
|
int lo = fromInclusive;
|
|
int hi = toExclusive;
|
|
while (lo < hi) {
|
|
// int mid = lo + ((hi - lo) >>> 1);
|
|
int mid = (lo & hi) + ((lo ^ hi) >> 1);
|
|
if (!predicate.test(mid)) {
|
|
lo = mid + 1;
|
|
} else {
|
|
hi = mid;
|
|
}
|
|
}
|
|
return hi;
|
|
}
|
|
|
|
public static double binarySearch(DoublePredicate predicate, double lo, double hi) {
|
|
for (int step = 0; step < 1000; step++) {
|
|
double mid = (lo + hi) / 2;
|
|
if (!predicate.test(mid)) {
|
|
lo = mid;
|
|
} else {
|
|
hi = mid;
|
|
}
|
|
}
|
|
return hi;
|
|
}
|
|
|
|
// random test
|
|
public static void main(String[] args) {
|
|
Random rnd = new Random(1);
|
|
for (int step = 0; step < 100_000; step++) {
|
|
int n = rnd.nextInt(20);
|
|
boolean[] b = new boolean[n];
|
|
int firstTrue = rnd.nextInt(n + 1);
|
|
Arrays.fill(b, firstTrue, n, true);
|
|
int res1 = binarySearchFirstTrueSimple(i -> b[i], 0, n - 1);
|
|
int res2 = binarySearchFirstTrue(i -> b[i], 0, n);
|
|
if (res1 != firstTrue || res1 != res2)
|
|
throw new RuntimeException();
|
|
}
|
|
|
|
System.out.println(Math.sqrt(2) == binarySearch(x -> x * x >= 2, 0, 2));
|
|
}
|
|
}
|