ZOJ 3279

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=3279

数状数组

#include <stdio.h>
#include <string.h>
#define lowbit(x) ((x)&(-x))
int n;
int a[100005],b[100005];
void update(int x,int v)
{
    while(x <= n)
    {
        a[x] += v;
        x += lowbit(x);
    }
}
int sum(int x)
{
    int ret = 0;
    while(x)
    {
        ret += a[x];
        x -= lowbit(x);
    }
    return ret;
}

int main()
{
    int i,m,x,y;
    char ch[2];
    while(scanf("%d",&n) ==1)
    {
        memset(a,0,sizeof(a));
        for(i = 1;i <= n;i ++)
        {
            scanf("%d",&b[i]);
            update(i,b[i]);
        }
        scanf("%d",&m);
        while(m --)
        {
            scanf("%s",ch);
            if(ch[0] == 'p')
            {
                scanf("%d %d",&x,&y);
                update(x,y-b[x]);
                b[x] = y;
            }
            else
            {
                scanf("%d",&x);
                int l=1;
                int r=n;
                int h;
                while(l<=r)
                {
                    h=(l+r)/2;
                    if(x>sum(h-1)&&x<=sum(h)) break;
                    if(x<=sum(h-1)) {r=h-1;continue;}
                    if(x>sum(h)) l=h+1;
                }
                printf("%d\n",h);
            }
        }
    }
    return 0;
}