HDU 4391 - Paint The Wall - 分块哈希入门

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>

using namespace std;

const int MAXN = 1e5+10;

struct HashBlock{
    int sizee, color;
    map<int, int> m;
} block[333];

int c[MAXN];
int len;
int n;

void Init()
{
    len = (int)sqrt(n);
    int tot = (n - 1) / len + 1;
    for(int i = 0; i < tot; i++) {
        block[i].sizee = min(n, (i+1) * len) - i * len;
        block[i].color = -1;
        block[i].m.clear();
    }
}

//如果一个区间要手动更新, 需要将上一次整块更新的颜色先覆盖, 再重新手动更新
//与线段树中pushdown异曲同工
void PushDown(int step)
{
    if(block[step].color != -1) {
        block[step].m.clear();
        for(int i = step * len; i < n && i < (step+1) * len; i++) {
            c[i] = block[step].color;
            block[step].m[c[i]]++;
        }
        block[step].color = -1;
    }
}

void Update(int l, int r, int color)
{
    int la = l / len, ra = r / len;
    //完整覆盖的区间可直接更新
    for(int i = la + 1; i < ra; i++) {
        block[i].color = color;
    }
    //暴力更新未被完整覆盖的部分
    if(la != ra) {
        PushDown(la), PushDown(ra);
        for(int i = l; i < (la+1) * len; i++) {
            block[la].m[c[i]]--, block[la].m[color]++, c[i] = color;
        }
        for(int i = ra * len; i <= r; i++) {
            block[ra].m[c[i]]--, block[ra].m[color]++, c[i] = color;
        }
    }
    else { //是同一段区间
        PushDown(la);
        for(int i = l; i <=r; i++) {
            block[la].m[c[i]]--, block[la].m[color]++, c[i] = color;
        }
    }
}

int Query(int l, int r, int color)
{
    int ans = 0;
    int la = l / len, ra = r / len;
    for(int i = la + 1; i < ra; i++) {
        if(block[i].color == color) ans += block[i].sizee;
        else if(block[i].color == -1 &&                 block[i].m.find(color) != block[i].m.end()) {
            ans += block[i].m[color];
        }
    }
    if(la != ra) {
        PushDown(la), PushDown(ra);
        for(int i = l; i < (la+1) * len; i++) {
            ans += c[i] == color;
        }
        for(int i = ra * len; i <= r; i++) {
            ans += c[i] == color;
        }
    }
    else {
        PushDown(la);
        for(int i = l; i <=r ; i++) {
            ans += c[i] == color;
        }
    }

    return ans;
}

int main()
{
    int q;

    while(scanf("%d %d", &n, &q) != EOF) {
        Init();
        for(int i = 0; i < n; i++) {
            scanf("%d", &c[i]);
            block[i/len].m[c[i]]++;
        }
        while(q--) {
            int cmd, l, r, z;
            scanf("%d %d %d %d", &cmd, &l, &r, &z);
            if(cmd == 1) Update(l, r, z);
            else printf("%d\n", Query(l, r, z));
        }
    }

    return 0;
}