c++/java/python 實現二分查找

c++/java/python 實現二分查找

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題目：尋找插入位置

給定一個已經升序排好序的數組，以及一個數target，如果target在數組中，返回它在數組中的位置。否則，返回target插入數組後它應該在的位置。
提示：輸入一個整數n，以及其對應的數組A[n]，最後輸入target

C++

#include <iostream>
#include <cstdio>
int searchInsert(int A[], int n, int target){
    int left = 0, right = n - 1;
    int mid;
    while(left < right){
        mid = (left + right) / 2;
        if(target <= A[mid]){
            right = mid;
        }else{
            left = mid + 1;
        }
    }
    if(target >= A[left]){
        left ++;
    }
    return left;
}

int main(){
    int n, target;
    scanf("%d", &n);
    int A[n];
    for(int i = 0; i < n; i++){
        scanf("%d", &A[i]);
    }
    scanf("%d", &target);
    printf("%d", searchInsert(A, n, target));
}

java

import java.util.Scanner;
public class Main{
    public int searchInsert(int[] A, int n, int target){
        int left = 0, right = n - 1, mid;
        while(left < right){
            mid = (left + right) / 2;
            if(target <= A[mid]){
                right = mid;
            }else{
                left = mid + 1;
            }
        }
        if(target > A[left]){
            left ++;
        }
        return left;
    }
    public static void main(String args[]){
        Main main = new Main();
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int[] A = new int[n];
        for(int i = 0; i < n; i++){
            A[i] = scan.nextInt();
        }
        int target = scan.nextInt();
        System.out.println(main.searchInsert(A, n, target));
    }
}

python

def searchInsert(A, n, target):
    left = 0
    right = n - 1
    while left < right:
        mid = (left + right) / 2
        if target <= A[mid]:
            right = mid
        else:
            left = mid + 1
    if target >= A[left]:
        left += 1
    return left

if __name__ == "__main__":
    n = int(raw_input())
    A = [int(i) for i in raw_input().split()]
    target = int(raw_input())
    print searchInsert(A, n, target)