题目
题解
线段树的板子题。注意两个题不太一样,HDU是多组数据,LG只有一组数据。
AC代码
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdlib>
#include<string>
#include<queue>
#include<map>
#include<stack>
#include<list>
#include<set>
#include<deque>
#include<vector>
#include<ctime>
using namespace std;
//#pragma GCC optimize(2)
#define IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define ull unsigned long long
#define ll long long
#define rep(i, x, y) for(int i=x;i<=y;i++)
#define mms(x, n) memset(x, n, sizeof(x))
#define mmc(a, b) memcpy(a, b, sizeof(b))
#define INF (0x3f3f3f3f)
#define mod (ull)(1e9+7)
typedef pair<int, int> P;
const int N = 2e5 + 10;
int n, m;
int A[N], Max[N * 4];
// 更新节点
void pushUp(int rt) {
Max[rt] = max(Max[rt << 1], Max[rt << 1 | 1]);
}
// 建树
void build(int l, int r, int rt) {
// 碰到叶子节点时,赋值
if (l == r) {
Max[rt] = A[l];
return;
}
int mid = (l + r) >> 1;
// 递归建树
build(l, mid, rt << 1);
build(mid + 1, r, rt << 1 | 1);
// 两个子树建立完成后更新当前节点的值
pushUp(rt);
}
// 单点更新
// [l, r]为当前区间
void udNode(int x, int c, int l, int r, int rt) {
if (l == r) {
if (Max[rt] < c) Max[rt] = c;
// Max[rt] = max(c, Max[rt]);
return;
}
int mid = (l + r) >> 1;
if (x <= mid) udNode(x, c, l, mid, rt << 1);
else udNode(x, c, mid + 1, r, rt << 1 | 1);
pushUp(rt);
}
//查询
// [L,R] 为目标区间, [l, r] 为当前区间
int Query(int L, int R, int l, int r, int rt) {
if (L <= l && r <= R) return Max[rt];
int mid = (l + r) >> 1;
int ans = -INF;
if (L <= mid) ans = max(ans, Query(L, R, l, mid, rt << 1));
if (R > mid) ans = max(ans, Query(L, R, mid + 1, r, rt << 1 | 1));
return ans;
}
int main() {
while (scanf("%d%d", &n, &m) != EOF) {
mms(A, 0);
mms(Max, 0);
for (int i = 1; i <= n; i++) scanf("%d", &A[i]);
build(1, n, 1);
char ch[2];
int a, b;
while (m--) {
scanf("%s%d%d", ch, &a, &b);
if (ch[0] == 'Q') {
printf("%d\n", Query(a, b, 1, n, 1));
} else udNode(a, b, 1, n, 1);
}
}
return 0;
}