Leetcode 463. Island Perimeter

You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water. Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells). The island doesn't have "lakes" (water inside that isn't connected to the water around the island). One cell is a square with side length 1. The grid is rectangular, width and height don't exceed 100. Determine the perimeter of the island.

Example:

[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

Answer: 16
Explanation: The perimeter is the 16 yellow stripes in the image below:

Code (Java):

class Solution {
    public int islandPerimeter(int[][] grid) {
        if (grid == null || grid.length == 0) {
            return 0;
        }
        
        int m = grid.length;
        int n = grid[0].length;
        
        int perimeter = 0;
        
        boolean[][] visited = new boolean[m][n];
        
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (visited[i][j] == false && grid[i][j] == 1) {
                    perimeter = islandPerimeterHelper(i, j, grid, visited);
                    break;
                }
            }
        }
        
        return perimeter;
    }
    
    private int islandPerimeterHelper(int row, int col, int[][] grid, boolean[][] visited) {
        int m = grid.length;
        int n = grid[0].length;
        
        if (row < 0 || row >= m || col < 0 || col >= n) {
            return 1;
        }
        
        if (grid[row][col] == 0) {
            return 1;
        }
        
        if (visited[row][col] == true) {
            return 0;
        }
        
        visited[row][col] = true;
        
        return islandPerimeterHelper(row - 1, col, grid, visited) + 
            islandPerimeterHelper(row + 1, col, grid, visited) + 
            islandPerimeterHelper(row, col - 1, grid, visited) + 
            islandPerimeterHelper(row, col + 1, grid, visited);
    }
}

Leetcode 657. Judge Route Circle

Initially, there is a Robot at position (0, 0). Given a sequence of its moves, judge if this robot makes a circle, which means it moves back to the original place.

The move sequence is represented by a string. And each move is represent by a character. The valid robot moves are R (Right), L(Left), U (Up) and D (down). The output should be true or false representing whether the robot makes a circle.

Example 1:

Input: "UD"
Output: true

Example 2:

Input: "LL"
Output: false

Code (Java):

class Solution {
    public boolean judgeCircle(String moves) {
        if (moves == null || moves.length() == 0) {
            return true;
        }
        
        int x = 0;
        int y = 0;
        
        for (int i = 0; i < moves.length(); i++) {
            char move = moves.charAt(i);
            switch (move) {
                case 'U':
                    y++;
                    break;
                case 'D':
                    y--;
                    break;
                case 'L':
                    x--;
                    break;
                case 'R':
                    x++;
                    break;
            }
        }
        
        return x == 0 && y == 0;
    }
}