洛谷OJ P3368 【模板】树状数组 2

题目链接：https://www.luogu.org/problemnew/show/P3368

题目思路：区间更新，单点查询模板题，树状数组做法

AC代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<string>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<queue>
#include<stack>
#include<map>

using namespace std;

#define FOU(i,x,y) for(int i=x;i<=y;i++)
#define FOD(i,x,y) for(int i=x;i>=y;i--)
#define MEM(a,val) memset(a,val,sizeof(a))
#define PI acos(-1.0)

const double EXP = 1e-9;
typedef long long ll;
typedef unsigned long long ull;
const int INF = 0x3f3f3f3f;
const ll MINF = 0x3f3f3f3f3f3f3f3f;
const double DINF = 0xffffffffffff;
const int mod = 1e9+7;
const int N = 1e6+5;

//一维树状数组区间修改，单点查询
//原来的值存在a[]里面，多建立个数组c1[](代码中用tree数组表示),注意：c1[i]=a[i]-a[i-1]。
//那么求a[i]的值的时候a[i]=a[i-1]+c1[i]=a[i-2]+c1[i]+c1[i-1]=…..=c1[1]+c1[2]+…+c1[i]。
int a[N],tree[N];
int n;
int lowbit(int x){return x&(-x);}
void updata(int x,int val){  //单点更新
    while(x<=n){
        tree[x]+=val;
        x+=lowbit(x);
    }
}
void regionUpdata(int x,int y,int val){ //区间更新，实现a[x]~a[y]+val
    updata(x,val);
    updata(y+1,-val);
}
int pointQuery(int x){  //单点查询,因为tree数组是差分数组，所以a[x]=tree[1]+tree[2]+...+tree[x]
    int ans=0;
    while(x>0){
        ans+=tree[x];
        x-=lowbit(x);
    }
    return ans;
}
void init(){
    a[0]=0;
    for(int i=1;i<=n;i++){
        updata(i,a[i]-a[i-1]);   //用差分数组初始化树状数组
    }
}

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    std::ios::sync_with_stdio(false);
    int q,x,y,val,typ;
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    init();
    while(q--){
        scanf("%d",&typ);
        if(typ==1){
            scanf("%d%d%d",&x,&y,&val);
            regionUpdata(x,y,val);
        }
        else{
            scanf("%d",&x);
            printf("%d\n",pointQuery(x));
        }
    }
    return 0;
}