查找之二折半查找（二分法查找）和插值查找

一、折半查找的前提是线性表中的记录必须好似关键码有序，线性表必须是顺序存储的。

二、折半查找

public class Binary_SearchDemo01 {
    static int[] num = {0,1,3,5};
    public static void main(String[] args) {
        int key = 3;
        int x = Sequential_Search(key);
        System.out.println(num[x]);
    }
    private static int Sequential_Search(int key) {
        int low,mid,high;
        low = 1;
        high = num.length-1;
        while(low <= high){
            mid = (low + high)/2;
            if(key<num[mid]){                
                high = mid-1;
            }    
            else if(key>num[mid]){
                low = mid+1;        
            }else{
                return mid;
            }
        }
        return 0;
    }
}

折半查找的时间复杂度为O(logn);