1754.I Hate it--线段树

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            int arr[] = new int[n + 1];
            int num = sc.nextInt();
            int tree[] = new int[(n + 5) * 4 + 1];
            for (int i = 1; i <= n; i++) {
                arr[i] = sc.nextInt();
            }
            create_tree(tree, arr, 0, 1, n);
            for (int i = 0; i < num; i++) {
                String s = sc.next();
                int a = sc.nextInt();
                int b = sc.nextInt();
                if (s.equals("Q")) {
                    System.out.println(querey(tree, arr, 0, 1, n, a, b));
                } else
                    update(tree, arr, 0, 1, n, a, b);
            }
        }
    }
    public static void create_tree(int tree[], int arr[], int node, int start, int end) {
        if (start == end)
            tree[node] = arr[start];
        else {
            int mid = (start + end) / 2;
            int left_node = node * 2 + 1;
            int right_node = node * 2 + 2;
            create_tree(tree, arr, left_node, start, mid);
            create_tree(tree, arr, right_node, mid + 1, end);
            tree[node] = Math.max(tree[left_node], tree[right_node]);
        }
    }
    public static void update(int tree[], int arr[], int node, int start, int end, int idx, int val) {
        if (start == end) {
            arr[start] = val; 
            tree[node] = val;
        } else {
            int mid = (start + end) / 2;
            int left_node = node * 2 + 1;
            int right_node = node * 2 + 2;
            if (start <= idx && idx <= mid)
                update(tree, arr, left_node, start, mid, idx, val);
            else if(idx = mid+1)
                update(tree, arr, right_node, mid + 1, end, idx, val);
            tree[node] = Math.max(tree[left_node], tree[right_node]);
        }
    }
    public static int querey(int tree[], int arr[], int node, int start, int end, int L, int R) {
        if (start > R || end < L)
            return 0;
        else if (start >= L && R >= end)
            return tree[node];
        else if (start == end)
            return tree[node];
        else {
            int mid = (start + end) / 2;
            int left_node = node * 2 + 1;
            int right_node = node * 2 + 2;
            int max_left = querey(tree, arr, left_node, start, mid, L, R);
            int max_right = querey(tree, arr, right_node, mid + 1, end, L, R);
            return Math.max(max_left, max_right);
        }
    }
}