kuangbin_SegTree B (HDU 1754)

跟A题类似 只是把update从增减直接改为赋值 query从求和改为求最大值 其他几乎一样

#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>
#define INF 0x3f3f3f3f
#define lson l, m, root<<1
#define rson m+1, r, root<<1|1
using namespace std;

const int MAXN = 2e5+10;
int val[MAXN*4];

void pushup(int root)
{
    val[root] = max(val[root<<1], val[root<<1|1]);
}

void build(int l, int r, int root)
{
    if(l == r) scanf("%d", &val[root]);
    else{
        int m = (l + r) >> 1;
        build(lson);
        build(rson);
        pushup(root);
    }
}

void update(int point, int value, int l, int r, int root)
{
    if(l == r) val[root] = value;
    else{
        int m = (l + r) >> 1;
        if(point <= m) update(point, value, lson);
        else update(point, value, rson);
        pushup(root);
    }
}

int query(int L, int R, int l, int r, int root)
{
    if(L <= l && R >= r) return val[root];
    int res = 0;
    int m = (l + r) >> 1;
    if(L <= m) res = max(res, query(L, R, lson));
    if(R > m) res = max(res, query(L, R, rson));
    return res;
}

int main()
{
    int n, m;
    while(~scanf("%d%d", &n, &m)){
        build(1, n, 1);
        char op[2];
        while(m--){
            scanf("%s", op);
            int u, v;
            scanf("%d%d", &u, &v);
            if(op[0] == 'U') update(u, v, 1, n, 1);
            else{
                if(u > v) swap(u, v);
                printf("%d\n", query(u, v, 1, n, 1));
            }
        }
    }
    return 0;
}