Java如何實現二分法查找

二分法查找

package com.epoch.createcarnumber.utils;

import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;

public class Dichotomy {
    private static int[] random() {
        int len = 5 + new Random().nextInt(6);
        int[] a = new int[len];
        for (int i = 0; i < a.length; i++) {
            a[i] = new Random().nextInt(100);
        }
        return a;
    }

    private static int binarySearch(int[] a, int t) {
        /*
         * 38
         *                mid
         * [1, 3, 30, 33, 38, 59, 61, 70, 85, 90]
         *  lo
         *                                    hi
         * 1.定義三個下標
         *   lo=0
         *   hi=a.length-1
         *   mid 先不賦值
         * 2.當lo<=hi
         * 3.計算中間位置mid=(lo+hi)/2
         * 4.mid位置的值>t，hi定位到mid-1位置
         * 5.mid位置的值<t，lo定位到mid+1位置
         * 6.否則，直接返回mid的值
         * 7.找不到數據，返回一個特殊值-1
         */
        int lo = 0;
        int hi = a.length - 1;
        int mid;
        while (lo <= hi) {
            mid = (lo + hi) / 2;
            if (a[mid] > t) {
                hi = mid - 1;
            }
            else if (a[mid] < t) {
                lo = mid + 1;
            }
            else {
                return mid;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] a = random();
        Arrays.sort(a);
        System.out.println(Arrays.toString(a));
        System.out.print("查找的目標值：");
        int t = new Scanner(System.in).nextInt();
        //二分法查找
        int index = binarySearch(a, t);
        System.out.println("你要查找的數字的下標爲："+index);
    }
}