摘要：A 对于一个子矩阵 \((x_1,y_1),(x_2,y_2)\)，其元素和为 \(\sum_{i=x_1}^{x_2}\sum_{j=y_1}^{y_2}S_i\cdot S_j=(\sum_{i=x_1}^{x_2}S_i)(\sum_{j=y_1}^{y_2}S_j)\)，\(O(n^2)\) 阅读全文