查找算法笔记(C++版)
记录最近学习的一些查找算法
1.顺序查找
时间复杂度:O(n)
代码:
//顺序查找
int sequentialSearch(int* list, int n, int x)
{
for (int i = 0; i < n; i++)
{
if (list[i] == x)
return i;
}
return -1;
}
测试代码:
int main(void)
{
int list[] = { 1,3,5,7,9,2,4,6,8,0 };//可以是无序数组
cout << "list[]:";
for (int i = 0; i < 10; i++)
cout << list[i] << " ";
cout << endl;
int x = 8;
int i = sequentialSearch(list, 10, x);
if (i < 0) cout << "未找到" << endl;
else cout << "list[" << i << "]中找到" << x << endl;
return 0;
}
运行结果:
list[]:1 3 5 7 9 2 4 6 8 0
list[8]中找到8
请按任意键继续. . .
2.二分查找
时间复杂度:O(logn)
代码:
//二分查找
int binSearch(int* list, int n, int x)
{
int lo = 0, hi = n - 1;
while (lo <= hi)
{
//int mid = (lo + hi) / 2;//此句代码在min和max很大时,会出现溢出!
int mid = (lo + ((hi - lo) >> 1));
if (x > list[mid])
lo = mid + 1;
else if(x < list[mid])
hi = mid - 1;
else //(x == list[mid])已找到
return mid;
}
return -1;
}
递归形式:
//二分查找(递归方式)
int binSearch_R(int* list, int lo, int hi, int x)
{
if (lo <= hi)
{
int mid = (lo + ((hi - lo) >> 1));
if (x > list[mid])
return(binSearch_R(list, mid + 1, hi, x));
else if (x < list[mid])
return(binSearch_R(list, lo, mid - 1, x));
else //(x == list[mid])已找到
return mid;
}
return -1;
}
测试代码:
int main(void)
{
int list[] = {1,3,5,7,9,11,13,15,17,19};//前提:有序数组!
cout << "list[]:";
for (int i = 0; i < 10;i++)
cout << list[i] << " ";
cout << endl;
int x = 15;
//int i = binSearch(list, 10, x);
int i = binSearch_R(list, 0, 10, x);
if (i < 0) cout << "未找到" << endl;
else cout << "list[" << i << "]中找到" << x << endl;
return 0;
}
运行结果:
list[]:1 3 5 7 9 11 13 15 17 19
list[7]中找到15
请按任意键继续. . .
来源:CSDN
作者:hbsyaaa
链接:https://blog.csdn.net/hbsyaaa/article/details/89787884