CodeForces Round #590 (Div 3)

1361 (+46), pupil
Rank: 1912（复兴号列车即将开动）

分析：树状数组题（比赛的时候忘了树状数组咋写了。。。）

代码：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 10;
char s[maxn];
int c[maxn][30];
int len;

int lowbit(int x)
{
    return x & (-x);
}

void ini()
{
    for(int i = 1; i <= len; i++)
        for(int j = i; j >= i - lowbit(i) + 1; j--)
            c[i][s[j] - 'a' + 1]++;
}

void update(int pos, char tar)
{
    for(int i = pos; i <= len; i += lowbit(i))
    {
        c[i][s[pos] - 'a' + 1]--;
        c[i][tar - 'a' + 1]++;
    }
    s[pos] = tar;
}
int sum(int a, int b)
{
    int res[30];
    memset(res, 0, sizeof(res));
    int ans = 0;
    for(int i = b; i >= 1; i -= lowbit(i))
        for(int j = 1; j <= 26; j++)
            res[j] += c[i][j];
    for(int i = a; i >= 1; i -= lowbit(i))
        for(int j = 1; j <= 26; j++)
            res[j] -= c[i][j];
    for(int i = 1; i <= 26; i++)
        if(res[i]) ans++;
    return ans;
}

int main()
{
    int ope;
    cin >> (s + 1);
    len = strlen(s + 1);
    int n; cin >> n;
    ini();
    while(n--)
    {
        scanf("%d", &ope);
        if(ope == 1)
        {
            int pos; scanf("%d", &pos);
            char x[10]; scanf("%s", x);
            update(pos, x[0]);
        }
        else
        {
            int a, b;
            scanf("%d%d", &a, &b);
            cout << sum(a - 1, b) << endl;
        }
    }
}