HDU 1698 Just a Hook

　　线段树成段更新的基础题，每次操作将x到y这个区间的值改为z，然后最后要求输出

的是1到n的区间和，根据线段树的性质，1到n的区间和其实就是sum[1]。

/*2012-08-08 16:07:20    Accepted    1698    1015MS    2280K    1407 B    G++    Yu*/
#include<stdio.h>

#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1

const int MAXN = 100100;
int sum[MAXN << 2], col[MAXN << 2];
int n, q;

void PushUp(int rt)
{
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
}

void PushDown(int l, int r, int rt)
{
    int m = l + r >> 1;
    if(col[rt])
    {
        col[rt << 1] = col[rt << 1 | 1] = col[rt];
        sum[rt << 1] = (m - l + 1) * col[rt];
        sum[rt << 1 | 1] = (r - m) * col[rt];
        col[rt] = 0;
    }
}

void build(int l, int r, int rt)
{
    col[rt] = 0;
    sum[rt] = 1;
    if(l == r) return;
    int m = l + r >> 1;
    build(lson);
    build(rson);
    PushUp(rt);
}

void update(int L, int R, int c, int l, int r, int rt)
{
    int m = l + r >> 1;
    if(L <= l && r <= R)
    {
        col[rt] = c;
        sum[rt] = (r - l + 1) * c;
        return;
    }
    PushDown(l, r, rt);
    if(L <= m) update(L, R, c, lson);
    if(R > m) update(L, R, c, rson);
    PushUp(rt);
}

int main()
{
    int T, cas = 1, x, y, z;
    scanf("%d", &T);
    for(cas = 1; cas <= T; cas ++)
    {
        scanf("%d%d", &n, &q);
        build(1, n, 1);
        while(q --)
        {
            scanf("%d%d%d", &x, &y, &z);
            update(x, y, z, 1, n, 1);
        }
        printf("Case %d: The total value of the hook is %d.\n", cas, sum[1]);
    }
    return 0;
}