AcWing 1264. 动态求连续区间和

线状数组

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 100010;

int n, m;
int a[N], tr[N];


int lowbit(int x){//取x的最后一位1
    return x& -x;
}
void add(int x,int y){//在x处加上y
    for(int i=x;i<=n;i+=lowbit(i)){
        tr[i]+=y;
    }
}
int query(int x){//查询第x位置的前缀和
    int res=0;
    for(int i=x;i;i-=lowbit(i))res+=tr[i];
    return res;
}
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i ++ ) scanf("%d", &a[i]);
    for (int i = 1; i <= n; i ++ ) add(i, a[i]);

    while (m -- )
    {
        int k, x, y;
        scanf("%d%d%d", &k, &x, &y);
        if (k == 0) printf("%d\n", query(y) - query(x - 1));
        else add(x, y);
    }

    return 0;
}

线段树

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 100010;

int n, m;
int w[N];
struct Node
{
    int l, r;
    int sum;
}tr[N * 4];

void pushup(int u)//更新u节点的sum值
{
    tr[u].sum = tr[u << 1].sum + tr[u << 1 | 1].sum;
}

void build(int u, int l, int r)//创建u节点，区间为l，r的树
{
    if (l == r) tr[u] = {l, r, w[r]};//如果已经是叶节点了，就直接赋值
    else
    {
        tr[u] = {l, r};
        int mid = l + r >> 1;
        build(u << 1, l, mid), build(u << 1 | 1, mid + 1, r);
        pushup(u);
    }
}

int query(int u, int l, int r)
{
    if (tr[u].l >= l && tr[u].r <= r) return tr[u].sum;//如果节点在查询区间内部，就直接返回sum
    int mid = tr[u].l + tr[u].r >> 1;
    int sum = 0;
    //判断是否在u的左右子树中
    if (l <= mid) sum = query(u << 1, l, r);
    if (r > mid) sum += query(u << 1 | 1, l, r);
    return sum;
}

void modify(int u, int x, int v)
{
    if (tr[u].l == tr[u].r) tr[u].sum += v;//如果已经是叶节点了，就直接修改sum
    else
    {
        int mid = tr[u].l + tr[u].r >> 1;
        if (x <= mid) modify(u << 1, x, v);
        else modify(u << 1 | 1, x, v);
        pushup(u);//在修改完u下的子节点后，再更新u
    }
}

int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i ++ ) scanf("%d", &w[i]);
    build(1, 1, n);

    int k, a, b;
    while (m -- )
    {
        scanf("%d%d%d", &k, &a, &b);
        if (k == 0) printf("%d\n", query(1, a, b));
        else modify(1, a, b);
    }

    return 0;
}