DFS
var numIslands = function(grid) { let m=grid.length; if(m==0) return 0; let n=grid[0].length; let direction=[[-1,0],[0,-1],[1,0],[0,1]]; let count=0; for(var i=0;i<m;i++){ for(var j=0;j<n;j++){ if(grid[i][j]=='1'){ dfs(grid,i,j); count++; } } } function dfs(grid,i,j){ if(i<0||i>=m||j<0||j>=n||grid[i][j]==0) return ; grid[i][j]=0; for(var k=0;k<4;k++) dfs(grid,i+direction[k][0],j+direction[k][1]); } return count; };
