查找

继续复习，先复习简单的顺序和二分查找

函数原型

//顺序查找
int seqSearch(data_t s[], data_t Key, int n){
    int i;
    i = 0;
    while (i < n && s[i] != Key)
        i++;

    if (s[i] == Key)
        return i;
    else
        return -1;
}

//对半查找-递归
int binarySearch_1(data_t s[], data_t x, int low, int high)
{
    int mid;
    if (low > high) return -1;
    mid = (low + high) / 2;
    if (x == s[mid])
        return mid;
    if (x < s[mid])
        return (binarySearch_1(s, x, low, mid - 1));
    else
        return (binarySearch_1(s, x, mid + 1, high));
}

//对半查找-非递归
int binarySearch_2(data_t s[], data_t x, int n)
{
    int mid, low, high;
    low = 0;
    high = n - 1;
    while (low <= n - 1) {
        mid = (low + high) / 2;
        if (s[mid] == x)
            return mid;
        else if (s[mid] < x)
            low = mid + 1;
        else 
            high = mid - 1;
    }
    return -1;
}

测试代码

int main(int argc, char *argv[])
{
    int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    int i;

//顺序查找    
    if ((i = seqSearch(a, 6, 10)) != -1) {
        printf("seqsearch: pos at %d 
", i);
    } else {
        printf("seqsearch error, no this key
");
    }
//对半查找-递归
    if ((i = binarySearch_1(a, 6, 0, 9)) != -1) {
        printf("binarySearch_1: pos at %d 
", i);
    } else {
        printf("binarySearch_1 error, no this key
");
    }
//对半查找-非递归
    if ((i = binarySearch_2(a, 6, 10)) != -1) {
        printf("binarySearch_2: pos at %d 
", i);
    } else {
        printf("binarysearch_2 error, no this key
");
    }
    
    return 0;
}

结果

seqsearch: pos at 6 
binarySearch_1: pos at 6 
binarySearch_2: pos at 6