merge没做可持久化为什么能通过

我只在split里写了可持久化，merge没改，也过了100pts，

void split(int cur, int v, int &x, int &y) {
    if(cur == 0) {
        x = y = 0;
        return;
    }
    if(val[cur] <= v) {
        x = addNode(val[cur]);
        pri[x] = pri[cur];
        chd[x][0] = chd[cur][0];
        split(chd[cur][1], v, chd[x][1], y);
        push_up(x);
    } else {
        y = addNode(val[cur]);
        pri[y] = pri[cur];
        chd[y][1] = chd[cur][1];
        split(chd[cur][0], v, x, chd[y][0]);
        push_up(y);
    }
}

int merge(int x, int y) {
    if(x == 0 || y == 0) return x | y;
    if(pri[x] > pri[y]) {
        chd[x][1] = merge(chd[x][1], y);
        push_up(x);
        return x;
    } else {
        chd[y][0] = merge(x, chd[y][0]);
        push_up(y);
        return y;
    }
}

完整代码

#include<iostream>
#include<random>
#include<ctime>
#define int long long
using namespace std;
const int N = 5E5 + 10;
const int INF = (int)0x3f3f3f3f3f3f3f3f;

int T;

mt19937 rng(time(NULL));

int val[50 * N], pri[50 * N], chd[50 * N][2], sz[50 * N], nn;
int root[N], vcnt;

void push_up(int p) {
    sz[p] = sz[chd[p][0]] + sz[chd[p][1]] + 1;
}

int addNode(int v) {
    val[++nn] = v;
    pri[nn] = rng();
    push_up(nn);
    return nn;
}

void split(int cur, int v, int &x, int &y) {
    if(cur == 0) {
        x = y = 0;
        return;
    }
    if(val[cur] <= v) {
        x = addNode(val[cur]);
        pri[x] = pri[cur];
        chd[x][0] = chd[cur][0];
        split(chd[cur][1], v, chd[x][1], y);
        push_up(x);
    } else {
        y = addNode(val[cur]);
        pri[y] = pri[cur];
        chd[y][1] = chd[cur][1];
        split(chd[cur][0], v, x, chd[y][0]);
        push_up(y);
    }
}

int merge(int x, int y) {
    if(x == 0 || y == 0) return x | y;
    if(pri[x] > pri[y]) {
        chd[x][1] = merge(chd[x][1], y);
        push_up(x);
        return x;
    } else {
        chd[y][0] = merge(x, chd[y][0]);
        push_up(y);
        return y;
    }
}

void insert(int v, int rt) {
    int x, y;
    split(root[rt], v, x, y);
    root[++vcnt] = merge(merge(x, addNode(v)), y);
}

void del(int v, int rt) {
    int x, y, z, w;
    split(root[rt], v - 1, x, w);
    split(w, v, y, z);
    root[++vcnt] = merge(merge(merge(x, chd[y][0]), chd[y][1]), z);
}

int queryRank(int v, int rt) {
    int cur = root[rt], res = 0;
    while(cur) {
        if(val[cur] >= v) {
            cur = chd[cur][0];
        } else {
            res += sz[chd[cur][0]] + 1;
            cur = chd[cur][1];
        }
    }
    return res;
}

int queryKth(int k, int rt) {
    int cur = root[rt], ans;
    while(cur) {
        ans = cur;
        if(k <= sz[chd[cur][0]]) {
            cur = chd[cur][0];
        } else if(k == sz[chd[cur][0]] + 1) return val[cur];
        else {
            k -= sz[chd[cur][0]] + 1;
            cur = chd[cur][1];
        }
    }
    return ans;
}

int pre(int v, int rt) {
    int cur = root[rt], res = -INF;
    while(cur) {
        if(val[cur] >= v) {
            cur = chd[cur][0];
        } else {
            res = max(res, val[cur]);
            cur = chd[cur][1];
        }
    }
    return res;
}

int suc(int v, int rt) {
    int cur = root[rt], res = INF;
    while(cur) {
        if(val[cur] <= v) {
            cur = chd[cur][1];
        } else {
            res = min(res, val[cur]);
            cur = chd[cur][0];
        }
    }
    return res;
}

signed main() {

    cin >> T;

    while(T--) {
        int op, v, x;
        cin >> v >> op >> x;
        if(op == 1) {
            insert(x, v);
        } else if(op == 2) {
            del(x, v);
        } else if(op == 3) {
            cout << queryRank(x, v) + 1 << '\n';
            root[++vcnt] = root[v];
        } else if(op == 4) {
            cout << queryKth(x, v) << '\n';
            root[++vcnt] = root[v];
        } else if(op == 5) {
            cout << pre(x, v) << '\n';
            root[++vcnt] = root[v];
        } else {
            cout << suc(x, v) << '\n';
            root[++vcnt] = root[v];
        }
    }

    return 0;
}