【Java】数组--二分法查找

代码

public class TestSearch{
    public static void main(String args[]){
        int[] a = {1,3,5,7,8,9,12,34,56,88};
        int i = 56;
        if(binarySearch(a,i) == -1)
            System.out.print("要查找的值不在源数据中！");
        else
            System.out.print("数据在数组中下标为"+binarySearch(a,i)+"的位置");
    }
    //二分查找法,建立在有序数组的基础上。
    public static int binarySearch(int[] a,int num){
        if(a.length==0) 
            return -1;     //-1表示没找到
        int startPos = 0;
        int endPos = a.length - 1;
        int m = (startPos + endPos) / 2; //int类型数据自动抹掉小数点，2.5即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; 
    }
}

简单的查找

public class TestSearch{
    public static void main(String args[]){
        int[] a = {1,3,5,7,8,9,12,34,56,88};
        int i = 12;
        if(search(a,i) == -1)
            System.out.print("要查找的值不在源数据中！");
        else
            System.out.print(search(a,i));
    }
    //从头到尾遍历查找
    public static int search(int[] a, int num) {
        for(int i=0; iif(a[i] == num) return i;
        }
        return -1;
    }
}

效果图