python/TangDou/AcWing/SegmentTree/P3919.cpp

#include <algorithm>
#include <cstdio>
#include <cmath>
#include <cstring>

using namespace std;
const int N = 1000010;

struct Node {
    int l, r, v;
} tr[N << 5];
int root[N], idx;
int n, m, a[N];

//快读
int read() {
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 3) + (x << 1) + (ch ^ 48);
        ch = getchar();
    }
    return x * f;
}

// build的原因，是因为有初始值，版本0不是空的
void build(int &u, int l, int r) {
    u = ++idx;
    if (l == r) {
        tr[u].v = a[l];
        return;
    }
    int mid = (l + r) >> 1;
    build(tr[u].l, l, mid);
    build(tr[u].r, mid + 1, r);
}

void update(int &u, int l, int r, int x, int v) {
    tr[++idx] = tr[u];
    u = idx;
    if (l == r) {
        tr[idx].v = v;
        return;
    }
    int mid = (l + r) >> 1;
    if (mid >= x)
        update(tr[u].l, l, mid, x, v);
    else
        update(tr[u].r, mid + 1, r, x, v);
}

int query(int u, int l, int r, int x) {
    if (l == r) return tr[u].v;
    int mid = (l + r) >> 1;
    if (mid >= x)
        return query(tr[u].l, l, mid, x);
    else
        return query(tr[u].r, mid + 1, r, x);
}
/*
答案：
59
87
41
87
88
46
*/
int main() {
//文件输入输出
#ifndef ONLINE_JUDGE
    freopen("P3919.in", "r", stdin);
#endif
    n = read(), m = read();
    for (int i = 1; i <= n; i++) a[i] = read();

    //构建主席树,因为有初始化值a[i]
    build(root[0], 1, n);

    for (int i = 1; i <= m; i++) {
        int x = read(), op = read(), y = read();
        if (op == 1) {
            // op=1:修改 x这个版本,管辖范围[1,n],将a[y]的值，即y这个位置,修改为v
            int v = read();
            root[i] = root[x];
            update(root[i], 1, n, y, v);
        } else {
            // op=2：访问版本x中，y这个位置上的值
            root[i] = root[x];
            printf("%d\n", query(root[i], 1, n, y));
        }
    }
    return 0;
}