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BinarySearch.java
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60 lines (54 loc) · 1.7 KB
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package interview.loop;
public class BinarySearch {
/**
* Searches element k in a sorted array.
* @param arr a sorted array
* @param k the element to search
* @return index in arr where k is. -1 if not found.
*/
public int binarySearch(int[] arr, int k) {
int a = 0;
int b = arr.length;
// Loop invariant: [a, b) is a valid range. (a <= b)
// k may only be within range [a, b).
while (a < b) {
int m = a + (b - a) / 2; // m = (a + b) / 2 may overflow!
if (k < arr[m]) {
b = m;
} else if (k > arr[m]) {
a = m + 1;
} else {
return m;
}
}
return -1;
}
public static void main(String[] args) {
BinarySearch bs = new BinarySearch();
System.out.println("Testing normal data");
System.out.println(
bs.binarySearch(new int[]{1, 2, 10, 15, 100}, 15));
System.out.println(
bs.binarySearch(new int[]{1, 2, 10, 15, 100}, -2));
System.out.println(
bs.binarySearch(new int[]{1, 2, 10, 15, 100}, 101));
System.out.println(
bs.binarySearch(new int[]{1, 2, 10, 15, 100}, 13));
System.out.println("======");
System.out.println("Testing empty or singleton data.");
System.out.println(
bs.binarySearch(new int[]{}, 13));
System.out.println(
bs.binarySearch(new int[]{12}, 13));
System.out.println(
bs.binarySearch(new int[]{13}, 13));
System.out.println("======");
System.out.println("Testing data of size 2.");
System.out.println(
bs.binarySearch(new int[]{12, 13}, 13));
System.out.println(
bs.binarySearch(new int[]{12, 13}, 12));
System.out.println(
bs.binarySearch(new int[]{12, 13}, 11));
}
}