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可持久化线段树

建树、单点修改、单点查询

#include <cstdio>
#include <cstring>
#include <algorithm>
#define MAXN (1000005*20)

int root[MAXN];

inline int read() {
    int flag = 1,num = 0; char ch = getchar();
    while(ch>'9'||ch<'0') {
        if(ch=='-') flag = -1;
        ch = getchar();
    }
    while(ch>='0'&&ch<='9') {
        num = num*10 + ch - 48;
        ch = getchar();
    }
    return num*flag;
}

class Persistent_Segment_Tree {
    
    private:
        int lson[MAXN],rson[MAXN],val[MAXN],cnt;
    public:
        void Build(int& rt,int l,int r) {
            rt = ++cnt;
            if(l==r) {
                val[rt] = read();
                return;
            }
            int mid = (l+r) >> 1;
            Build(lson[rt],l,mid); Build(rson[rt],mid+1,r);
        }
        void update(int& rt,int pre,int l,int r,int x,int value) {
            rt = ++cnt; val[rt] = val[pre];
            lson[rt] = lson[pre]; rson[rt] = rson[pre];
            if(l==r) {
                val[rt] = value;
                return;
            }
            int mid = (l+r)>>1;
            if(x<=mid) update(lson[rt],lson[pre],l,mid,x,value);
            else update(rson[rt],rson[pre],mid+1,r,x,value);
        }
        int query(int rt,int l,int r,int x) {
            if(l==r) return val[rt];
            int mid = (l+r) >> 1;
            if(x<=mid) return query(lson[rt],l,mid,x);
            else return query(rson[rt],mid+1,r,x);
        }
}T;

int N,M;

int main() {

    N = read(); M = read();
    T.Build(root[0],1,N);

    int pre,opt,x,value;
    for(int i=1;i<=M;++i) {
        scanf("%d%d",&pre,&opt);
        if(opt==1) {
            scanf("%d%d",&x,&value);
            T.update(root[i],root[pre],1,N,x,value);
        }
        else {
            scanf("%d",&x);
            printf("%d\n",T.query(root[pre],1,N,x));
            root[i] = root[pre];
        }
    }

    return 0;
}