C++实现线段树(lazy-tag方法)-区间修改，区间查询

代码如下：

#include <iostream>
using namespace std;
const int N = 10010;
typedef long long LL;
LL input[N];struct node {int l, r;LL sum;LL add;
} tree[4 * N];void build(int l, int r, int u) {tree[u].l = l;tree[u].r = r;if (l == r) {tree[u].sum = input[l];return ;}int mid = (l + r) >> 1;build(l, mid, 2 * u);build(mid + 1, r, 2 * u + 1);tree[u].sum = tree[2 * u].sum + tree[2 * u + 1].sum;
}void spread(int u) {if (tree[u].add) //当lazy tag不为0时，说明当前区间已经被这个影响所作用，//这个区间的所有子区间全都攒着工作没有修改{tree[2 * u].add += tree[u].add;tree[2 * u + 1].add += tree[u].add;tree[2 * u].sum += tree[u].add * (tree[2 * u].r - tree[2 * u].l + 1);tree[2 * u + 1].sum += tree[u].add * (tree[2 * u + 1].r - tree[2 * u + 1].l + 1);tree[u].add = 0;}
}void update(int cl, int cr, int w, int u) {if (tree[u].l >= cl && tree[u].r <= cr) {tree[u].sum += (LL)w * (tree[u].r - tree[u].l + 1);tree[u].add += (LL)w;return ;}spread(u);int mid = (tree[u].l + tree[u].r) >> 1;if (cl <= mid)update(cl, cr, w, 2 * u);if (cr > mid)//不能写成(cr >= mid)，不然可能会死循环update(cl, cr, w, 2 * u + 1);tree[u].sum = tree[2 * u].sum + tree[2 * u + 1].sum;
}LL query(int cl, int cr, int u) {if (tree[u].l >= cl && tree[u].r <= cr)return tree[u].sum;spread(u);int mid = (tree[u].l + tree[u].r) >> 1;LL ans = 0;if (cl <= mid)ans += query(cl, cr, 2 * u);if (cr > mid)ans += query(cl, cr, 2 * u + 1);
//	cout << ans << endl;return ans;
}int main() {int n;cin >> n;for (int i = 1; i <= n; i++)cin >> input[i];build(1, n, 1);cout << query(3, 6, 1) << endl;//查询区间[3,6]所有元素之和update(3, 6, 3, 1);//给区间[3,6]所有元素加上3cout << query(3, 6, 1) << endl;//再次查询区间[3,6]所有元素之和return 0;
}