AcWing 796. 子矩陣的和 (Prefix Sum) Describted by Java

Today train Prefix sum , two dimensional is a little complex than one dimensional,but it is not a big deal. The problem: 輸入一個n行m列的整數矩陣，再輸入q個詢問，每一個詢問包含四個整數x1, y1, x2, y2，表示一個子矩陣的左上角座標和右下角座標。java 對於每一個詢

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