Category: Recursion

Categories
Leetcode Recursion

Happy Number

let isHappy = function(n) {
    let visited = {};

    function sumOfSquare(num) {
        if (visited[num]) return false;
        visited[num] = true;

        let sum = 0;
        while (num > 0) {
            let d = num % 10; //?
            num = Math.floor(num / 10); //?
            sum += d * d;
        }

        if (sum === 1) {
            return true;
        }
        else {
            return sumOfSquare(sum);
        }
    }
    
    return sumOfSquare(n);
};
Categories
Leetcode Recursion

Unique Paths (Recursion)

let uniquePaths = function(m, n) {
    let results = new Set();
    function getPath(row, col, path = '') {
        if (row >= m && col >= n) {
            results.add(path);
            return;
        }

        if (row === m) {
            // go right if at the bottom row
            getPath(row, col + 1, path + 'R');
        }
        else if (col === n) {
            // go down if at the end column
            getPath(row + 1, col, path + 'D');
        }
        else {
            // go down and go right
            getPath(row, col + 1, path + 'R');
            getPath(row + 1, col, path + 'D');
        }
    }

    getPath(1, 1, 'S');
    return results.size;
};
Categories
Leetcode Recursion

Minimum Path Sum (Recursion)

let minPathSum = function(grid) {

    if(!grid || !grid.length) return 0;

    let maxRow = grid.length, maxCol = grid[0].length;
    function sum(row, col, total, path = '') {
        const val = grid[row][col] + total; //?
        if (row === maxRow - 1 && col === maxCol - 1) {
            return val;
        } //?

        if (row === maxRow - 1) {
            return sum(row, col + 1, val);
        }
        else if (col === maxCol - 1) {
            return sum(row + 1, col, val);
        } else {
            const down = sum(row + 1, col, val);
            const right = sum(row, col + 1, val);
            return Math.min(down, right);
        }
    }

    return sum(0, 0, 0);
};
Categories
Binary Tree Depth First Search Leetcode Recursion

Path Sum II

let pathSum = function(root, sum, results = [], result = []) {

    if (!root) return results;
    if (sum - root.val === 0 && !root.left && !root.right) {
        results.push([...result, root.val]);
    }

    pathSum(root.left, sum - root.val, results, [...result, root.val]);
    pathSum(root.right, sum - root.val, results, [...result, root.val]);
    return results;
};
Categories
Binary Tree Depth First Search Leetcode Recursion

Path Sum I

let hasPathSum = function(root, sum) {

    if (!root) return false;
    if (sum - root.val === 0 && !root.left && !root.right) return true;

    return hasPathSum(root.left, sum - root.val)
        || hasPathSum(root.right, sum - root.val);
};
Categories
Depth First Search Leetcode Recursion

Minesweeper

let updateBoard = function(board, click) {

    let maxRow = board.length,
        maxCol = board[0].length,
        MINE = 'M',
        BLANK = 'B',
        EMPTY = 'E',
        GAMEOVER = 'X';

    function isMine(row, col) {
        if (row < 0 || col < 0 || row >= maxRow || col >= maxCol) {
            return 0;
        }
        return board[row][col] === MINE ? 1 : 0;
    }

    function getMineCount(row, col) {
        let nearbyMines = 0;
        nearbyMines += isMine(row - 1, col - 1); // top left
        nearbyMines += isMine(row - 1, col); // top
        nearbyMines += isMine(row - 1, col + 1); // top right
        nearbyMines += isMine(row, col - 1); // left
        nearbyMines += isMine(row, col + 1); // right
        nearbyMines += isMine(row + 1, col - 1); // bottom left
        nearbyMines += isMine(row + 1, col); // bottom
        nearbyMines += isMine(row + 1, col + 1); // bottom right
        return nearbyMines;
    }

    function markAndExplore(row, col) {
        if (row < 0 || col < 0 || row >= maxRow || col >= maxCol) {
            return;
        }
        const data = board[row][col];
        if (data === EMPTY) {

            const mineCount = getMineCount(row, col);
            board[row][col] = mineCount > 0 ? `${mineCount}` : BLANK;

            if (mineCount === 0) {
                markAndExplore(row - 1, col - 1); // top left
                markAndExplore(row - 1, col); // top
                markAndExplore(row - 1, col + 1); // top right
                markAndExplore(row, col - 1); // left
                markAndExplore(row, col + 1); // right
                markAndExplore(row + 1, col - 1); // bottom left
                markAndExplore(row + 1, col); // bottom
                markAndExplore(row + 1, col + 1); // bottom right
            }
        }
    }

    let [x, y] = click;
    if (board[x][y] === MINE) {
        board[x][y] = GAMEOVER;
    }
    else {
        markAndExplore(x, y);
    }

    return board;
};
Categories
Depth First Search Leetcode Loop Recursion

Island Perimeter

let islandPerimeter = function(grid) {

    if (!grid || !grid.length) return 0;

    let maxRow = grid.length,
        maxCol = grid[0].length,
        LAND = 1, VISITED = 2;

    function calculatePerimeter(row, col) {

        if (grid[row][col] === LAND) {
            grid[row][col] = VISITED;

            let perimeter = 4;
            // check above;
            if (row > 0
                && (grid[row - 1][col] === LAND || grid[row - 1][col] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row - 1, col);
            }

            // check below;
            if (row < maxRow - 1
                && (grid[row + 1][col] === LAND || grid[row + 1][col] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row + 1, col);
            }

            // check left;
            if (col > 0
                && (grid[row][col - 1] === LAND || grid[row][col - 1] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row, col - 1);
            }

            // check right;
            if (col < maxCol - 1
                && (grid[row][col + 1] === LAND || grid[row][col + 1] === VISITED)) {
                perimeter = perimeter - 1;
                perimeter += calculatePerimeter(row, col + 1);
            }

            return perimeter; //?
        }

        return 0;
    }

    for (let row = 0; row < maxRow; row++) {
        for (let col = 0; col < maxCol;col++) {
            if (grid[row][col] === LAND) {
                return calculatePerimeter(row, col);
            }
        }
    }

    return 0;

};
Categories
Depth First Search Leetcode Recursion

Max Area of Island

let maxAreaOfIsland = function(grid) {

    if (!grid || !grid.length) return 0;

    let max = 0,
        maxRow = grid.length,
        maxCol = grid[0].length,
        LAND = 1, VISITED = 2;

    function markAndGetTotal(row, col) {
        if (row < 0 || row >= maxRow || col < 0 || col >= maxCol) return 0;
        if (grid[row][col] === LAND) {
            grid[row][col] = VISITED;

            let result = 1;
            // top
            result += markAndGetTotal(row - 1, col);
            // bottom
            result += markAndGetTotal(row + 1, col);
            // left
            result += markAndGetTotal(row, col - 1);
            /// right
            result += markAndGetTotal(row, col + 1);
            return result;
        }
        return 0;
    }

    for (let row = 0; row < maxRow;row++) {
        for (let col = 0; col < maxCol;col++) {
            if (grid[row][col] === LAND) {
                const total = markAndGetTotal(row, col); //?
                max = Math.max(total, max);
            }
        }
    }

    return max;
};
Categories
Depth First Search Leetcode Loop Matrix Recursion

Number Of Distinct Islands

if (!grid || !grid.length) return 0;

let numRows = grid.length,
    numCols = grid[0].length,
    LAND = 1, VISITED = 2;

function markAndVisit(row, col, island = [], level = 0) {
    if (grid[row][col] === LAND) {
        grid[row][col] = VISITED;
        island.push('X' + level);

        // up
        if (row > 0 && grid[row - 1][col] === LAND) {
            island.push('U' + level);
            markAndVisit(row - 1, col, island, level + 1);
        }

        // down
        if (row < numRows - 1 && grid[row + 1][col] === LAND) {
            island.push('D' + level);
            markAndVisit(row + 1, col, island, level + 1);
        }

        // left
        if (col > 0 && grid[row][col - 1] === LAND) {
            island.push('L' + level);
            markAndVisit(row, col - 1, island, level + 1);
        }

        // right
        if (col < numCols - 1 && grid && grid[row][col + 1] === LAND) {
            island.push('R' + level);
            markAndVisit(row, col + 1, island, level + 1);
        }
    }

    return island;
}

let islands = new Set();
for (let row = 0; row < numRows;row++) {
    for (let col = 0; col < numCols;col++) {
        if (grid[row][col] === LAND) {
            let island = markAndVisit(row, col);
            // console.log(island);
            if (island.length) islands.add(island.join(''));
        }
    }
}

// console.table(grid);
return islands.size;
Categories
Binary Tree Leetcode Recursion

Is Subtree

let isSubtree = function(mainTree, subTree) {

    function isSame(left, right) {
        if (left === right) return true;
        if (left === null && right !== null) return false;
        if (left !== null && right === null) return false;
        if (left.val !== right.val) return false;
        return isSame(left.left, right.left)
            && isSame(left.right, right.right);
    }

    if (mainTree === subTree) return true;
    if (!mainTree) return false;
    if (isSame(mainTree, subTree)) return true;

    return isSubtree(mainTree.left, subTree) || isSubtree(mainTree.right, subTree);
};