1

#include <bits/stdc++.h>
using namespace std;
string s;
int main()
{
    cin >> s;
    bool flag = true; //一开始认为回文
    //检查每个对称位置
    for (int i = 0, j = s.length() - 1; i < j; i++, j--)
        if (s[i] != s[j])
        {
            flag = false;
            break;
        }
    if (flag)
        cout << "yes\n";
    else
        cout << "no\n";
    return 0;
}

2

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin >> s;
    bool flag = true; // 一开始认为回文
    // 检查每个位置
    for (int i = 0; i < s.length(); i++)
        // i 对应的回文位置为 s.length()-1-i
        if (s[i] != s[s.length() - 1 - i])
        {
            flag = false;
            break;
        }
    if (flag)
        cout << "yes\n";
    else
        cout << "no\n";
    return 0;
}

3

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin >> s;

    // 处理出逆序之后的 s
    string t;
    t = s;
    for (int i = 0, j = t.length() - 1; i <= j; i++, j--)
        swap(t[i], t[j]);

    if (s == t)
        cout << "yes\n";
    else
        cout << "no\n";
    return 0;
}

4

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin >> s;

    // 处理出逆序之后的 s
    string t;
    t = s;
    reverse(t.begin(), t.end());

    if (s == t)
        cout << "yes\n";
    else
        cout << "no\n";
    return 0;
}