80分，调了wa的样例答案是对的，为啥？？

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

/*P1104 生日*/
struct oi {
    string s;
    int y, m, d;
}a[105];

bool cmp(oi a, oi b) {
    if (a.y < b.y) return true;
    else if (a.y == b.y && a.m < b.m) return true;
    else if (a.y == b.y && a.m == b.m && a.d < b.d) return true;
    else return false;
}
int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        cin >> a[i].s >> a[i].y >> a[i].m >> a[i].d;
    }
    sort(a + 1, a + 1 + n, cmp);
    for (int i = 1; i <= n; ++i) {
        cout << a[i].s << endl;
    }
    return 0;
}