线段树--单点更新

#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;

const int maxn = 55555;
int sum[maxn*4];
void PushUp(int rt)
{
sum[rt] = sum[rt*2] + sum[rt*2+1];//求区间和
sum[rt] = max(sum[rt*2],sum[rt*2+1]);//求区间最大值
}

void build(int l, int r, int rt)//建立线段树
{
if (l == r)
{
scanf("%d", &sum[rt]);
return;
}
int m = (l + r) / 2;
build(l, m, rt*2);
build(m + 1, r, rt*2+1);
PushUp(rt);
}

void update(int p, int add, int l, int r, int rt)
{
if (l == r)
{
sum[rt] += add;
return;
}
int m = (l + r) / 2;
if (p <= m)
update(p, add, l, m, rt*2);
else
update(p, add, m + 1, r, rt*2+1);

PushUp(rt);
}

int query(int ll, int rr, int l, int r, int rt)//查询线段树
{
if (ll <= l && rr >= r)
return sum[rt];
int m = (l + r) / 2;
int ans = 0;
if (ll <= m)
ans += query(ll, rr, l, m, rt*2);
if (rr > m)
ans += query(ll, rr, m + 1, r, rt*2+1);
return ans;
}

int main(void)
{
int t, c;
char d[10];
scanf("%d", &t);
for (c = 1; c <= t; c++)
{
printf("Case %d:\n", c);
int n;
scanf("%d", &n);
build(1, n, 1);
while (scanf("%s", d) != EOF)
{
if (d[0] == 'E') break;
int x, y;
scanf("%d%d", &x, &y);
if (d[0] == 'Q')
{
int ans = query(x, y, 1, n, 1);
printf("%d\n", ans);
}
if (d[0] == 'S') update(x, -y, 1, n, 1);
if (d[0] == 'A') update(x, y, 1, n, 1);
}
}
return 0;
}