markdown Ex1.1.22

Posted 2021-05-06

package com.test;


public class BinarySearch {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        System.out.println(binarySearch(arr, 9));
    }

    private static int binarySearch(int[] arr, int key) {
        int lo = 0;
        int hi = arr.length - 1;
        while (lo <= hi) {
            int mid = lo + (hi - lo) / 2;
            if (key < arr[mid]) {
                hi = mid - 1;
            } else if (key > arr[mid]) {
                lo = mid + 1;
            } else {
                return mid;
            }
        }
        return -1;
    }
    private static int binarySearch2(int[] arr,int key,int lo,int hi,int level) {
        // 递归实现
        // 打印递归深度
        for (int i = 0;i< level;i++) {
            System.out.print("    ");
        }
        System.out.printf("lo:%d hi:%d level:%d\n",lo,hi,level);

        if (lo > hi) {
            return -1;
        }
        int mid = lo+(hi - lo) / 2;
        if (key < arr[mid] ){
            return binarySearch2(arr,key,lo,mid - 1,++level);
        } else if (key > arr[mid]) {
            return binarySearch2(arr,key,mid + 1,hi,++level);
        } else {
            return mid;
        }
    }
}

def binary_search(arr: list, key: int) -> int:
    lo = 0
    hi = len(arr) - 1
    while lo <= hi:
        mid = lo + (hi - lo) // 2
        if key < arr[mid]:
            hi = mid - 1
        elif key > arr[mid]:
            lo = mid + 1
        else:
            return mid
    return -1


def binary_search2(arr: list, key: int, lo: int, hi: int, level: int) ->int:
    # 递归实现
    # 打印递归深度
    print("{:s}lo:{:d} hi:{:d} level:{:d}".format("    " * level, lo, hi, level))

    if lo > hi:
        return -1
    mid = lo + (hi - lo) // 2
    if key < arr[mid]:
        return binary_search2(arr, key, lo, mid - 1, level + 1)
    elif key > arr[mid]:
        return binary_search2(arr, key, mid + 1, hi, level + 1)
    else:
        return mid


if __name__ == '__main__':
    arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
    print(binary_search2(arr, 9, 0, len(arr)-1, 0))

package main

import "fmt"

func main() {
    arr := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
    fmt.Println(BinarySearch2(arr, 9, 0, len(arr)-1, 0))
}
func BinarySearch(arr []int, key int) (int) {
    lo := 0
    hi := len(arr) - 1
    for lo <= hi {
        mid := lo + (hi-lo)/2
        if key < arr[mid] {
            hi = mid - 1
        } else if key > arr[mid] {
            lo = mid + 1
        } else {
            return mid
        }
    }
    return -1
}
func BinarySearch2(arr []int, key, lo, hi, level int) int {
    // 递归实现
    // 打印递归深度
    for i := 0; i < level; i++ {
        fmt.Print("    ")
    }
    fmt.Printf("lo:%d hi:%d level:%d\n", lo, hi, level)

    if lo > hi {
        return -1
    }
    mid := lo + (hi-lo)/2
    if key < arr[mid] {
        return BinarySearch2(arr, key, lo, mid-1, level+1)
    } else if key > arr[mid] {
        return BinarySearch2(arr, key, mid+1, hi, level+1)
    } else {
        return mid
    }

}

二分搜索的时间复杂度为 O(log n)