hdu1754 I Hate It

题目链接：hdu1754 I Hate It

树状数组学习参考博客：http://blog.csdn.net/u010598215/article/details/48206959

树状数组之前没看懂就放着一直没看了,现在抽空学下...

#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#define CLR(a,b) memset((a),(b),sizeof((a)))
using namespace std;
typedef long long ll;
const int N = 200001;
int n;
int a[N];
int tree[N];
int lowbit(int x){
    return x&(-x);
}
void update(int pos){
    int lx, i;
    while(pos <= n){
        tree[pos] = a[pos];
        lx = lowbit(pos);
        for(i = 1; i < lx; i <<= 1)
            tree[pos] = max(tree[pos], tree[pos-i]);
        pos += lowbit(i);
    }
}
int query_ma(int x, int y){
    int ma = 0;
    while(y >= x){
        ma = max(ma, a[y]);
        y--;
        for(; y - lowbit(y) >= x; y -= lowbit(y))
            ma = max(tree[y], ma);
    }
    return ma;
}
int main(){
    int m, i;
    while(~scanf("%d%d", &n, &m)){
        CLR(tree, 0);
        for(i = 1; i <= n; ++i){
            scanf("%d", &a[i]);
            update(i);
        }
        int l, r;
        char c;
        while(m--){
            scanf("%*c%c%d%d", &c, &l, &r);
            if(c == 'Q')
                printf("%d\n", query_ma(l,r));
            else {
                a[l] = r;
                update(l);
            }
        }
    }
    return 0;
}