HDU 1698 Just a Hook——区间更新的线段树

题意：一开始有n个1组成的数列，执行q此操作，每次操作给出x y z，表示把区间【x，y】内的所有数变成z，执行完q此操作后求整个数列的和

思路：直接套用区间更新线段树的模板，进行简单的更新值与求和操作

#include 
#include 
#include 
#include 

using namespace std;

const int maxn = 1e5 + 10;

int T, n, q, date[maxn], segTree[maxn<<2], lazy[maxn<<2];

void init() {
    for (int i = 1; i <= n; i++) {
        date[i] = 1;
    }
    for (int i = 1; i <= n<<2; i++) {
        segTree[i] = 0;
        lazy[i] = 0;
    }
}

void pushup(int root) {
    segTree[root] = segTree[root<<1] + segTree[root<<1|1];
}

void pushdown(int root, int cntL, int cntR) {
    if (lazy[root]) {
        lazy[root<<1] = lazy[root];
        lazy[root<<1|1] = lazy[root];
        segTree[root<<1] = lazy[root] * cntL;
        segTree[root<<1|1] = lazy[root] * cntR;
        lazy[root] = 0;
    }
}

void build(int L, int R, int root) {
    if (L == R) {
        segTree[root] = date[L];
        return;
    }
    int mid = (L + R)>>1;
    build(L, mid, root<<1);
    build(mid + 1, R, root<<1|1);
    pushup(root);
}

void update_interval(int L, int R, int root, int uL, int uR, int val) {
    if (uL <= L && R <= uR) {
        segTree[root] = val * (R - L + 1);
        lazy[root] = val;
        return;
    }
    int mid = (L + R)>>1;
    pushdown(root, mid - L + 1, R - mid);
    if (uL <= mid) {
        update_interval(L, mid, root<<1, uL, uR, val);
    }
    if (uR > mid) {
        update_interval(mid + 1, R, root<<1|1, uL, uR, val);
    }
    pushup(root);
}

int query(int L, int R, int root, int qL, int qR) {
    if (qL <= L && R <= qR) {
        return segTree[root];
    }
    int mid = (L + R)>>1;
    pushdown(root, mid - L + 1, R - mid);
    int ans = 0;
    if (qL <= mid) {
        ans += query(L, mid, root<<1, qL, qR);
    }
    if (qR > mid) {
        ans += query(mid + 1, R, root<<1|1, qL, qR);
    }
    return ans;
}

int main()
{
    scanf("%d", &T);
    for (int kase = 1; kase <= T; kase++) {
        scanf("%d%d", &n, &q);
        init();
        build(1, n, 1);
        while (q--) {
            int a, b, c; scanf("%d %d %d", &a, &b, &c);
            update_interval(1, n, 1, a, b, c);
        }
        printf("Case %d: The total value of the hook is %d.\n", kase, query(1, n, 1, 1, n));
    }
    return 0;
}