初写线段树的时候，印象最深的一道，有一个pushdown的操作，使我的tle变成了ac
题意
输入t，然后t组数据
输入n，m，n代表n个点上价值全是1的绳子，m代表m次操作
m行l，r，val 就是区间l，r变成val
求最后绳子总共价值
思路
线段树，懒人标记
#include<queue> #include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<map> #include<cmath> #include<string> #include<vector> #include<functional> #define inf 0x3f3f3f3f #define mem(k,b) memset(k,b,sizeof(k)) #define ll long long #define ls (x)<<1 #define rs (x)<<1|1 #define lson ls,l,mid #define rson rs,mid+1,r using namespace std; const int maxn = 100010; int t, n, m, q, p, z; int tree[maxn << 2], add[maxn << 2]; void pushup(int x) { tree[x] = tree[ls] + tree[rs]; return; } void pushdown(int x, int len){ if (add[x]){ add[ls] = add[x]; add[rs] = add[x]; tree[ls] = add[x] * (len - (len >> 1)); tree[rs] = add[x] * (len >> 1); add[x] = 0; } } void build(int x, int l, int r){ add[x] = 0; if (l == r){ tree[x] = 1; return; } int mid = (l + r) >> 1; build(lson); build(rson); pushup(x); } void xiugai(int x, int l, int r, int l1, int r1,int zhi1){ if (l >= l1 && r<=r1){ add[x] = zhi1; tree[x] = zhi1*(r - l + 1); return; } pushdown(x, r - l + 1); int mid = (l + r) >> 1; if (r1<= mid){ xiugai(lson, l1, r1, zhi1); } else if (l1>mid){ xiugai(rson, l1, r1, zhi1); } else{ xiugai(lson, l1, mid, zhi1); xiugai(rson, mid + 1, r1, zhi1); } pushup(x); } int main(){ int c = 1; scanf("%d",&t); while (t--){ scanf("%d%d",&n,&m); build(1, 1, n); for (int i = 0; i < m; i++){ scanf("%d%d%d",&q,&p,&z); xiugai(1, 1, n, q, p, z); } printf("Case %d: The total value of the hook is %d. ",c++,tree[1]); } return 0; }