【HDU1754】I Hate It（线段树）

update:单点替换 query:区间最值

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <numeric>
#include <cctype>
#include <algorithm>
#include <cmath>
#include <vector>
#include <climits>
using namespace std;

const int maxn = 2e5 + 10;
int maxv[maxn * 3];

void update (int p, int v, int o, int L, int R) {
    int M = L + ((R - L) >> 1);
    if (L == R) {
        maxv[o] = v;
    } else {
        if (p <= M) {
            update (p, v, o << 1, L, M);
        } else {
            update (p, v, (o << 1) | 1, M + 1, R);
        }
        maxv[o] = max (maxv[o * 2], maxv[o << 1 | 1]);
    }
}

int query (int ql, int qr, int o, int L, int R) {
    int M = L + (R - L) / 2, ans = INT_MIN;
    if (ql <= L && R <= qr) {
        return maxv[o];
    }
    if (ql <= M) {
        ans = max (ans, query (ql, qr, o << 1, L, M));
    }
    if (M < qr) {
        ans = max (ans, query (ql, qr, o << 1 | 1, M + 1, R));
    }
    return ans;
}

int main () {
    int n, ask_n, x, a, b;
    char op[5];
    while (~scanf ("%d%d", &n, &ask_n)) {
        memset (maxv, 0, sizeof(maxv));
        for (int i = 1; i <= n; ++ i)  {
            scanf ("%d", &x);
            update (i, x, 1, 1, n);
        }

        while (ask_n --) {
            scanf ("%s %d %d", op, &a, &b);

            if (op[0] == 'Q') {
                printf ("%d
", query (a, b, 1, 1, n));
            } else if (op[0] == 'U') {
                update (a, b, 1, 1, n);
            }
        }
    }
    return 0;
}