二分探索(Binary Search)

C

#include <stdio.h>

int binarySearch(int arr[], int l, int r, int x) {
    while (l <= r) {
        int m = l + (r - l) / 2;

        if (arr[m] == x) {
            return m;
        }

        if (arr[m] < x) {
            l = m + 1;
        } else {
            r = m - 1;
        }
    }
    return -1;
}

int main() {
    int arr[] = {2, 3, 4, 10, 40};
    int n = sizeof(arr) / sizeof(arr[0]);
    int x = 10;
    int result = binarySearch(arr, 0, n - 1, x);
    (result == -1) ? printf("Element not found\n") : printf("Element found at index %d\n", result);
    return 0;
}

C++

#include <iostream>
using namespace std;

int binarySearch(int arr[], int l, int r, int x) {
    while (l <= r) {
        int m = l + (r - l) / 2;

        if (arr[m] == x) {
            return m;
        }

        if (arr[m] < x) {
            l = m + 1;
        } else {
            r = m - 1;
        }
    }
    return -1;
}

int main() {
    int arr[] = {2, 3, 4, 10, 40};
    int n = sizeof(arr) / sizeof(arr[0]);
    int x = 10;
    int result = binarySearch(arr, 0, n - 1, x);
    (result == -1) ? cout << "Element not found" << endl : cout << "Element found at index " << result << endl;
    return 0;
}

C#

using System;

class Program {
    static int BinarySearch(int[] arr, int x) {
        int l = 0, r = arr.Length - 1;
        while (l <= r) {
            int m = l + (r - l) / 2;

            if (arr[m] == x) {
                return m;
            }

            if (arr[m] < x) {
                l = m + 1;
            } else {
                r = m - 1;
            }
        }
        return -1;
    }

    static void Main() {
        int[] arr = {2, 3, 4, 10, 40};
        int x = 10;
        int result = BinarySearch(arr, x);
        Console.WriteLine(result == -1 ? "Element not found" : "Element found at index " + result);
    }
}

Java

public class BinarySearch {
    public static int binarySearch(int[] arr, int x) {
        int l = 0, r = arr.length - 1;
        while (l <= r) {
            int m = l + (r - l) / 2;

            if (arr[m] == x) {
                return m;
            }

            if (arr[m] < x) {
                l = m + 1;
            } else {
                r = m - 1;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] arr = {2, 3, 4, 10, 40};
        int x = 10;
        int result = binarySearch(arr, x);
        System.out.println(result == -1 ? "Element not found" : "Element found at index " + result);
    }
}

Python

def binary_search(arr, x):
    l, r = 0, len(arr) - 1
    while l <= r:
        m = l + (r - l) // 2

        if arr[m] == x:
            return m

        if arr[m] < x:
            l = m + 1
        else:
            r = m - 1
    return -1

arr = [2, 3, 4, 10, 40]
x = 10
result = binary_search(arr, x)
print("Element found at index" if result != -1 else "Element not found", result)

JavaScript

function binarySearch(arr, x) {
    let l = 0, r = arr.length - 1;
    while (l <= r) {
        let m = l + Math.floor((r - l) / 2);

        if (arr[m] === x) {
            return m;
        }

        if (arr[m] < x) {
            l = m + 1;
        } else {
            r = m - 1;
        }
    }
    return -1;
}

const arr = [2, 3, 4, 10, 40];
const x = 10;
const result = binarySearch(arr, x);
console.log(result === -1 ? "Element not found" : "Element found at index " + result);