字典树模板+初始化模板

https://codeforces.com/contest/1658/problem/D2

int l, r;
int son[M][2], idx;
int a[N];

void init() {//初始化**
    idx = 0;
    son[0][0] = son[0][1] = 0;
}

void insert(int x) {
    int p = 0;
    for (int i = 30; ~i; i --) {
        int &v = son[p][x >> i & 1];
        if (!v) {
            son[idx + 1][0] = son[idx + 1][1] = 0;//初始化*****
            v = ++ idx;
        }
        p = v;
    }
}

int findmax(int x) {
    int p = 0, ans = 0;
    for (int i = 30; ~i; i --) {
        int v = x >> i & 1;
        if (son[p][!v]) {
            ans += 1 << i;
            p = son[p][!v];
        }
        else p = son[p][v];
    }
    return ans;
}

int findmin(int x) {
    int p = 0, ans = 0;
    for (int i = 30; ~i; i --) {
        int v = x >> i & 1;
        if (son[p][v]) p = son[p][v];
        else {
            ans += 1 << i;
            p = son[p][!v];
        }
    }
    return ans;
}

void solve() {
    cin >> l >> r;

    init();
    for (int i = l; i <= r; i ++) cin >> a[i], insert(a[i]);

    for (int i = l; i <= r; i ++) {
        int x = a[i] ^ l;

        if (findmin(x) == l && findmax(x) == r) {
            cout << x << endl;
            return;
        }
    }
}