写法1:借助”数的范围”找边界的思想
#include <iostream>
using namespace std;
const int N = 100010;
int n,m;
int a[N];
int main()
{
cin >> n >> m;
for(int i = 1; i <= n; i++)
{
cin >> a[i];
}
while(m--)
{
int x; cin >> x;
int l = 1, r = n;
while(l < r)
{
int mid = (l + r) / 2;
if(a[mid] >= x)
{
r = mid;
}
else
{
l = mid + 1;
}
}
if(a[l] != x)
{
cout << "-1" << " ";
}
else
{
cout << l << " ";
}
}
return 0;
}
写法2:官方写法
#include <iostream>
using namespace std;
const int N = 100010;
int a[N];
int main()
{
int n; cin >> n; // 定义数组大小
for(int i = 1; i <= n; i++)
{
cin >> a[i];
}
int x; cin >> x;
int l = 0, r = n;
int flag = 0; // 用于标记是否找到了答案
while(l <= r)
{
int mid = (l + r) / 2;
if(a[mid] == x)
{
cout << mid << endl;
flag = 1;
break;
}
else if(a[mid] > x)
{
r = mid - 1;
}
else if(a[mid] < x)
{
l = mid + 1;
}
}
if(flag == 0)
{
cout << "-1" << endl;
}
return 0;
}