1754.I Hate it--线段树

线段树三个主要方法的模板

import java.util.*;
public class Main {
	// main
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int tree[] = new int[1000];
		int arr[] = { 0, 1, 3, 5, 7, 9, 11 };
		// for (int i = 1; i < length; i++) { //存储数据
		// arr[i] = sc.nextInt();
		// }
		create_tree(arr, tree, 0, 1, arr.length - 1); // 这里记得减1 因为arr[]是从0开始存储数据
		for (int i = 0; i < tree.length; i++) {
			System.out.print(tree[i] + " ");
		}
		System.out.println();
		update(arr, tree, 0, 1, arr.length - 1, 5, 6);
		for (int i = 0; i < tree.length; i++) {
			System.out.print(tree[i] + " ");
		}System.out.println();
		System.out.println(querey(tree, arr, 0, 1, 6, 2, 5));
	
	}
	// create
	public static void create_tree(int arr[], int tree[], int node, int start, int end) { // create建树方法！！！
		if (start == end) { // 离散化的点进行调整！！！
			tree[node] = arr[start];
		} else {
			int left_node = 2 * node + 1; // 0 | 1 2 | 3 4 5 6 ...........
			int right_node = 2 * node + 2;
			int mid = (start + end) / 2;
			create_tree(arr, tree, left_node, start, mid);
			create_tree(arr, tree, right_node, mid + 1, end);
			tree[node] = tree[left_node] + tree[right_node]; // 核心代码
		}
	}
	// update
	public static void update(int arr[], int tree[], int node, int start, int end, int idx, int val) {
		if (start == end) {
			arr[start] = val;
			tree[node] = val;
		} else {
			int left_node = 2 * node + 1; // 0 | 1 2 | 3 4 5 6 ...........
			int right_node = 2 * node + 2;
			int mid = (start + end) / 2;
			if (idx <= mid && idx >= start) {
				update(arr, tree, left_node, start, mid, idx, val);
			} else if (idx <= end && idx >= mid + 1) {
				update(arr, tree, right_node, mid + 1, end, idx, val);
			}
			tree[node] = tree[left_node] + tree[right_node]; // 核心代码
		}
	}
	// querey
	public static int querey(int tree[], int arr[], int node, int start, int end, int L, int R) {
		if (R < start || end < L) { // 排除范围之外
			return 0;
		} else if (L <= start && end <= R)
			return tree[node];
		else if (start == end)
			return node;
		else {
			int mid = (start + end) / 2;
			int left_node = node * 2 + 1;
			int right_node = node * 2 + 2;
			int sum_left = querey(tree, arr, left_node, start, mid, L, R);
			int sum_right = querey(tree, arr, right_node, mid + 1, end, L, R);
			return sum_left + sum_right;
		}
	}
}

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 <= end && 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);
		}
	}
}