计蒜客 - A1603.天上的星星

二维差分,理论上很简单,虽然我实际上做的时候一堆问题

1.边界的星星包含在内,需要在减去的时候往前挪一个

2.我是从0开始的,循环的时候非常不方便

3.x1, x2, y1, y2总是弄混

#include <cstdio>
using namespace std;
const int N = ;
int sum[N][N];
int main() {
    int n;
    scanf("%d", &n);
    for (int i = ; i < n; i++) {
        int x, y, w;
        scanf("%d %d %d", &x, &y, &w);
        sum[x][y] += w;
    }
    for (int i = ; i < N; i++) {
        sum[i][] = sum[i][] + sum[i - ][];
        sum[][i] = sum[][i] + sum[][i - ];
    }

    for (int i = ; i < N; i++)
        for (int j = ; j < N; j++)
            sum[i][j] = sum[i][j] + sum[i - ][j] + sum[i][j - ] - sum[i - ][j - ];
    int q;
    scanf("%d", &q);
    while (q--) {
        int x1, y1, x2, y2;
        scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
        int ans;
        if (x1 >  && y1 > )
            ans = sum[x2][y2] - sum[x2][y1 - ] - sum[x1 - ][y2] + sum[x1 - ][y1 - ];
        else if (x1 ==  && y1 != )
            ans = sum[x2][y2] - sum[x2][y1 - ];
        else if (x1 > )
            ans = sum[x2][y2] - sum[x1 - ][y2];
        else
            ans = sum[x2][y2];
        printf("%d\n", ans);
    }
    return ;
}