給你一個由 '1'（陸地）和 '0'（水）組成的的二維網(wǎng)格，請你計算網(wǎng)格中島嶼的數(shù)量。

島嶼總是被水包圍，并且每座島嶼只能由水平方向和/或豎直方向上相鄰的陸地連接形成。

此外，你可以假設該網(wǎng)格的四條邊均被水包圍。

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示例 1：

輸入：grid = [

? ["1","1","1","1","0"],

? ["1","1","0","1","0"],

? ["1","1","0","0","0"],

? ["0","0","0","0","0"]

]

輸出：1

示例 2：

輸入：grid = [

? ["1","1","0","0","0"],

? ["1","1","0","0","0"],

? ["0","0","1","0","0"],

? ["0","0","0","1","1"]

]

輸出：3

通過遍歷矩陣，找到每個島嶼的起點，然后通過“感染函數(shù)”將其周圍的所有相鄰的1都標記為2。這樣，每找到一個起點，就可以將它所在的島嶼的所有1都標記為2，最終島嶼的數(shù)量就是所有起點的數(shù)量。