题解 | #【模板】二维前缀和#

【模板】二维前缀和

https://www.nowcoder.com/practice/99eb8040d116414ea3296467ce81cbbc

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        int n = in.nextInt();
        int m = in.nextInt();
        int q = in.nextInt();
        long[][] arr = new long[n][m];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (i == 0 && j == 0) {
                    arr[i][j] = in.nextLong();
                }
                else if (i == 0) {
                    arr[i][j] = in.nextLong() + arr[i][j-1];
                }
                else if (j == 0) {
                    arr[i][j] = in.nextLong() + arr[i-1][j];
                }
                else {
                    arr[i][j] = in.nextLong() - arr[i-1][j-1] + 
                    arr[i-1][j] + arr[i][j-1];
                }
            }
        }

        for (int i = 0; i < q; i++) {
            int x1 = in.nextInt()-1;
            int y1 = in.nextInt()-1;
            int x2 = in.nextInt()-1;
            int y2 = in.nextInt()-1;
            if (x1 == 0 && y1 == 0) {
                System.out.println(arr[x2][y2]);
            }
            else if (x1 == 0) {
                System.out.println(arr[x2][y2]-arr[x2][y1-1]);
            }
            else if (y1 == 0) {
                System.out.println(arr[x2][y2]-arr[x1-1][y2]);
            }
            else {
                System.out.println(arr[x2][y2]-arr[x2][y1-1]-arr[x1-1][y2]+arr[x1-1][y1-1]);
            }
        }
    }
}

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