二分法search

从基础做起

public class TestSearch {
public static void main(String[] args){
int a[] = {1,3,6,8,9,10,12,18,20,34};
int i = 12;
System.out.println(binarySearch(a,i));
}

public static int binarySearch(int[]a, int num){
if(a.length == 0) return -1;

int startPos = 0;
int endPos = a.length - 1;
int m = (startPos + endPos)/2;
while(startPos <= endPos){
if(num == a[m]) return m;
if(num > a[m]){
startPos = m + 1;
}
if(num < a[m]){
endPos = m -1;
}
m = (startPos + endPos)/2;
}
return -1;
}
}