[Noip2018普及组]对称二叉树

#include<cstdio>
#define max(a,b) ((a)>(b)?(a):(b))
const int MAXN = 1000000;
int siz[MAXN + 5], le[MAXN + 5], ri[MAXN + 5], v[MAXN + 5], ans;
bool check(int r1, int r2) {
    if( v[r1] != v[r2] ) return false;
    else if( r1 == 0 && r2 == 0 ) return true;
    else return check(le[r1], ri[r2]) && check(ri[r1], le[r2]);
}
int dfs1(int rt) {
    if( !rt ) return 0;
    else return siz[rt] = dfs1(le[rt]) + dfs1(ri[rt]) + 1;
}
void dfs2(int rt) {
    if( !rt ) return ;
    if( siz[le[rt]] == siz[ri[rt]] )
        if( check(le[rt], ri[rt]) ) ans = max(ans, siz[rt]);
    dfs2(le[rt]), dfs2(ri[rt]);
}
int main() {
    int n; v[0] = -1;
    scanf("%d", &n);
    for(int i=1;i<=n;i++)
        scanf("%d", &v[i]);
    for(int i=1;i<=n;i++) {
        scanf("%d%d", &le[i], &ri[i]);
        if( le[i] == -1 ) le[i] = 0;
        if( ri[i] == -1 ) ri[i] = 0;
    }
    dfs1(1), dfs2(1);
    printf("%d\n", ans);
}