leetcode200.島嶼數量

題目

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

島嶼總是被水包圍，並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線形成。

此外，你可以假設該網格的四條邊均被水包圍。

用例

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

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
 

求解

/**
 * @param {character[][]} grid
 * @return {number}
 */
var numIslands = function(grid) {
    let res = 0
    for(let i=0;i<grid.length;i++){
        for(let j=0;j<grid[0].length;j++){
            //發現未被訪問過，且是陸地的部分,進行深度優先遍歷，沉沒陸地
            if(grid[i][j]==1){
                res++
                dfs(i,j)
            }
        }
    }
    return res

    //深度優先遍歷
    function dfs(i,j){
        if(grid[i][j]==0){
            return
        }
        //沉沒當前陸地
        grid[i][j]=0
        if(i-1>=0) dfs(i-1,j)
        if(j-1>=0) dfs(i,j-1)
        if(i+1<grid.length) dfs(i+1,j)
        if(j+1<grid[0].length) dfs(i,j+1)
    }
};