線段樹功能:update:成段替換

成段更新去要用到延遲標記，具體調試代碼就容易懂些

#include <iostream>
#include <string>
#include <cstdio>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
using namespace std;

const int MAXN = 111111;
int sum[MAXN<<2], chg[MAXN<<2];//sum表示區間和，chg數組：非0就需要將它的兒子更新，更新是在下一次查詢更新
 


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

void push_down(int rt, int len)
{
    if(chg[rt] == 0) return;
    chg[rt<<1] = chg[rt<<1|1] = chg[rt];
    sum[rt<<1] = (len - (len >> 1)) * chg[rt];
    sum[rt<<1|1] = (len >> 1
 
) * chg[rt];
    chg[rt] = 0;
}

void build(int l, int r, int rt)
{
    sum[rt] = 1;    //也可以寫在return語句前，不影響結果
    chg[rt] = 0;
    if(l == r) return;
    int m = (l + r) >> 1;
    build(lson);
    build(rson);
    push_up(rt);
}

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

int main()
{
    int T, Case = 0;
    scanf("%d", &T);
    while(T--)
    {
        int N, Q;
        scanf("%d%d", &N, &Q);
        build(1, N, 1);
        while(Q--)
        {
            int X, Y, Z;
            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", ++Case, sum[1]);
    }
    return 0;
}

hdu 1698 Just a Hook 線段樹成段更新