数据结构--查找

1、顺序查找

package com.chazhao;

public class Main {

    public static void main(String[] args) {

        int[] arr={110,2,23,4,65,6,17,8,9,10,11,21,53,24,35,16};
        int result=getIndex(arr, 10);
        System.out.println(result);

    }

    /**
     * 顺序查找
     * @param arr
     * @param value
     * @return
     */
    public static int getIndex(int[] arr, int value){

        for (int i = 0; i < arr.length; i++) {
            if (value == arr[i]){
                return i;
            }
        }
        return -1;
    }

}

2、有序表查找

前提--有序表

package com.chazhao;

public class Main2 {

    public static void main(String[] args) {

        int[] arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};
        int result=getIndex(arr, 11);
        System.out.println(result);
        int result2=getIndex2(arr, 11);
        System.out.println(result2);
    }

    /**
     * 折半查找
     * 思想：取中间的比较对象，如果给定值与比较对象相等，则查找成功；如果给定值小与比较对象，
     * 则在比较对象左办区查找；否则在右半区查找
     * @param arr
     * @param value
     * @return
     */
    public static int getIndex(int[] arr, int value){

        int left=0, right=arr.length-1;
        int middle;
        while (left <= right){
            middle=(left+right)/2;
            int tmp=arr[middle];
            if (tmp == value){
                return middle;
            }else if (tmp < value){
                left=middle+1;
            }else if(tmp > value){
                right=middle-1;
            }
        }
        return -1;
    }

    /**
     * 插值查找
     *思想：对折半查找的优化，仅去middle的值的方式不同
     * 
     * 如果查找一个不存在很大的数据，插值查找会导致数组越界异常
     * @param arr
     * @param value
     * @return
     */
    public static int getIndex2(int[] arr, int value){

        int left=0, right=arr.length-1;
        int middle;
        while (left < right){
            middle=left+(right-left)*(value-arr[left])/(arr[right]-arr[left]);
            int tmp=arr[middle];
            if (tmp == value){
                return middle;
            }else if (tmp < value){
                left=middle+1;
            }else if(tmp > value){
                right=middle-1;
            }
        }
        return -1;
    }
}