查找

查找

查找元素伪代码

穷举法
Begin
    Set num[length] to some number
    Set target
    Set i to 0
    read target
    while (i <length) do
        if(num[i] == target)
            printf("找到了")
            break
    if(i==length)
        printf("没找到")
二分法
Begin
    Set num[length] to some number
    Set target，left，right
    Set i to 0
    Set left to num[0]
    Set right to num[length-1]
    read target
    while(left<=right)
        Set mid to (left+right)/2
        if(num[mid]>target)
            right to mid -1
        if(num[mid]<target)
            left to mid +1
        if(num[mid]==target)
            printf("找到了")
    if(left > right)
        printf("找不到")
End  

代码实现

二分法代码（仅以该数组和7为例子）
#include <stdio.h>
int main()
{
    int arr[10]={1,2,3,4,5,6,7,8,9,10} ;
    int left = 0 ;
    int right = 0 ;
    int a = 7 ;
    int i = 1 ;
    int n = sizeof(arr) / sizeof(arr[0]) ;
    right = n - 1 ;
    while (left <= right)
{
    int mid = (left+right)/2 ;
    if (arr[mid]> a)
    {
        right = mid - 1 ;
    }
    if (arr[mid]< a)
    {
        left = mid + 1 ;
    }
    if (arr[mid]==a)
    {
        printf("找到了,下标是：%d",mid);
        break;
    }
    
    }
    if (left > right )
    {
        printf("找不到") ;
    }

    return 0 ;
}