更小的数 参考代码

#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
const int maxn = 5000 + 100;
int n, ans;
char str[maxn];
int dp[maxn][maxn];

int main() {
#ifdef ExRoc
    freopen("test.txt", "r", stdin);
#endif // ExRoc
    ios::sync_with_stdio(false);

    cin >> (str + 1);
    n = strlen(str + 1);
    for (int len = 1; len <= n; ++len) {
        for (int l = 1; l + len - 1 <= n; ++l) {
            int r = l + len - 1;
            if (str[r] < str[l]) {
                dp[l][r] = 1;
            } else if (str[r] > str[l]) {
                dp[l][r] = -1;
            } else {
                dp[l][r] = dp[l + 1][r - 1];
            }
            if (dp[l][r] == 1) {
                ++ans;
            }
        }
    }
    cout << ans << endl;

    return 0;
}