UVA 12086 - Potentiometers(树状数组)

UVA 12086 - Potentiometers

题目链接

题意：一个序列，两种操作，某个位置值变成x，询问l，r区间的和

思路：树状数组搞

代码：

#include <cstdio>
#include <cstring>

#define lowbit(x) (x&(-x))

const int N = 200005;

int n, bit
, num
;

void add(int x, int v) {
while (x <= n) {
bit[x] += v;
x += lowbit(x);
}
}

int query(int x) {
int ans = 0;
while (x) {
ans += bit[x];
x -= lowbit(x);
}
return ans;
}

int query(int l, int r) {
return query(r) - query(l - 1);
}

int main() {
int cas = 0;
while (~scanf("%d", &n) && n) {
if (cas) printf("\n");
int a, b;
memset(bit, 0, sizeof(bit));
for (int i = 1; i <= n; i++) {
scanf("%d", &num[i]);
add(i, num[i]);
}
char Q[10];
printf("Case %d:\n", ++cas);
while (~scanf("%s", Q) && Q[0] != 'E') {
scanf("%d%d", &a, &b);
if (Q[0] == 'M')
printf("%d\n", query(a, b));
else {
add(a, b - num[a]);
num[a] = b;
}
}
}
return 0;
}