先用线段树做了一下，结果用cin超时，数据太变态了，此题正解应该是倍增算法。
先看看线段树怎么做这题；
如果不懂线段树的先看此视频：https://www.bilibili.com/video/BV1cb411t7AM?from=search&seid=13093045061996989240
1.线段树：
1 #include <iostream> 2 #include <algorithm> 3 #include <cstdio> 4 using namespace std; 5 6 constexpr size_t N = 4e5 + 10; 7 int arr[N], tree[N]; 8 9 void build_tree(int node, int start, int end) { 10 if (start == end) { 11 tree[node] = arr[start]; 12 return; 13 } 14 int mid = (start + end) >> 1; 15 int left_node = node << 1; 16 int right_node = (node << 1) + 1; 17 build_tree(left_node, start, mid); 18 build_tree(right_node, mid + 1, end); 19 20 tree[node] = max(tree[left_node], tree[right_node]); 21 } 22 23 int query_tree(int node, int start, int end, int L, int R) { 24 if (L > end || R < start) 25 return 0; 26 else if (L <= start && end <= R) 27 return tree[node]; 28 int mid = (start + end) >> 1; 29 int left_node = node << 1; 30 int right_node = (node << 1 ) + 1; 31 int left_max = query_tree(left_node, start, mid, L, R); 32 int right_max = query_tree(right_node, mid + 1, end, L, R); 33 return max(left_max, right_max); 34 } 35 36 int main() { 37 38 int n, m; 39 scanf("%d%d", &n, &m); 40 for (int i = 1; i <= n; ++i) scanf("%d",&arr[i]); 41 build_tree(1, 1, n); 42 while (m--) { 43 int L, R; 44 scanf("%d%d", &L, &R); 45 printf("%d ",query_tree(1, 1, n, L, R)); 46 } 47 }
2.倍增算法（ST）：
倍增看lyd
：https://www.bilibili.com/video/BV14t411t73D?from=search&seid=17507997773809817751
1 #include <iostream> 2 #include <algorithm> 3 using namespace std; 4 5 constexpr size_t N = 2e5 + 5; 6 int dp[N][30]; 7 int a[N]; 8 int n, m; 9 10 void getRMQ() { 11 for(int i = 1; i <= n; ++ i) dp[i][0] = a[i]; 12 for (int j = 1; (1 << j) <= n; ++j) { 13 for (int i = 1; i + (1 << j) - 1 <= n; ++i) { 14 dp[i][j] = max(dp[i][j - 1], dp[i + (1 << (j - 1))][j - 1]); 15 } 16 } 17 } 18 int RMQmax(int l, int r) { 19 int k = 0; 20 while ((1 << (k + 1)) <= r - l + 1) ++k; 21 return max(dp[l][k], dp[r - (1 << k) + 1][k]); 22 } 23 24 int main() { 25 scanf("%d%d", &n, &m); 26 for(int i = 1; i <= n; ++ i) scanf("%d", &a[i]); 27 getRMQ(); 28 int l, r; 29 while(m--) { 30 scanf("%d%d", &l, &r); 31 printf("%d ", RMQmax(l, r)); 32 } 33 return 0; 34 35 } 36