纪念逝去的岁月——C/C++二分查找

代码

#include <stdio.h>

int binarySearch(int iList[], int iNum, int iX, int * pPos)
{
    if(NULL == pPos)
    {
        return -1;
    }
    int i = 0, j = iNum;
    while(i < j)
    {
        printf("from [%d] to [%d]\n", i, j);
        int iPos = (i + j) / 2;
        int iMid = iList[iPos];
        if(iX == iMid)
        {
            *pPos = iPos;
            return 0;
        }
        else if (iX > iMid)
        {
            i = iPos + 1;
        }
        else
        {
            j = iPos - 1;
        }
    }
    if(iList[i] == iX)
    {
        *pPos = i;
        return 0;
    }
    *pPos = -1;
    return -1;
}

int main(int argc ,char * argv[])
{
    int iList[33] = {0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33};
    int iPos = 0;
    int iNum = 33;

    int iX = 5;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    iX = 6;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    iX = 0;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    iX = 33;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    iX = -1;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    iX = 35;
    binarySearch(iList, iNum, iX, &iPos);
    printf("[%d] @ position [%d]\n\n", iX, iPos);

    return 0;
}

编译

$ g++ -o binarySearch binarySearch.cpp

运行

$ ./binarySearch 
from [0] to [33]
from [0] to [15]
from [0] to [6]
from [4] to [6]
[5] @ position [5]

from [0] to [33]
from [0] to [15]
from [0] to [6]
from [4] to [6]
[6] @ position [-1]

from [0] to [33]
from [0] to [15]
from [0] to [6]
from [0] to [2]
[0] @ position [0]

from [0] to [33]
from [17] to [33]
from [26] to [33]
from [30] to [33]
from [32] to [33]
[33] @ position [32]

from [0] to [33]
from [0] to [15]
from [0] to [6]
from [0] to [2]
[-1] @ position [-1]

from [0] to [33]
from [17] to [33]
from [26] to [33]
from [30] to [33]
from [32] to [33]
[35] @ position [-1]

再见……