(See subfolders for individual solutions)
function generateSubsets(nums, start = 0, subset = [], result = []) {
result.push([...subset]);
for (let i = start; i < nums.length; i++) {
subset.push(nums[i]);
generateSubsets(nums, i + 1, subset, result);
subset.pop();
}
return result;
}- Notes: Useful for problems that involve generating all subsets, or powersets, from a given set. Also applicable for finding specific subsets, like those that sum to a certain target.
- Example LeetCode Problems:
function permute(nums, start = 0, result = []) {
if (start === nums.length - 1) {
result.push([...nums]);
}
for (let i = start; i < nums.length; i++) {
[nums[start], nums[i]] = [nums[i], nums[start]];
permute(nums, start + 1, result);
[nums[start], nums[i]] = [nums[i], nums[start]]; // backtrack
}
return result;
}- Notes: Used when you need to generate all possible orders or arrangements of a set of elements. It's often useful in problems that involve strings or arrays.
- Example LeetCode Problems:
function combine(nums, k, start = 0, combination = [], result = []) {
if (combination.length === k) {
result.push([...combination]);
return;
}
for (let i = start; i < nums.length; i++) {
combination.push(nums[i]);
combine(nums, k, i + 1, combination, result);
combination.pop();
}
return result;
}- Notes: Used for problems that involve generating all combinations of k elements from a given set. This pattern can also be adapted for problems that require generating combinations that meet a certain criteria.
- Example LeetCode Problems:
function solveNQueens(n) {
const board = Array.from({ length: n }, () => Array(n).fill('.'));
const result = [];
function isValid(row, col) {
// Check same column
for (let i = 0; i < row; i++) {
if (board[i][col] === 'Q') return false;
}
// Check diagonals
for (let i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
if (board[i][j] === 'Q') return false;
}
for (let i = row - 1, j = col + 1; i >= 0 && j < n; i--, j++) {
if (board[i][j] === 'Q') return false;
}
return true;
}
function backtrack(row = 0) {
if (row === n) {
result.push(board.map(r => r.join('')));
return;
}
for (let col = 0; col < n; col++) {
if (isValid(row, col)) {
board[row][col] = 'Q';
backtrack(row + 1);
board[row][col] = '.'; // backtrack
}
}
}
backtrack();
return result;
}- Notes: Although specifically for N-Queens, this pattern shows how to handle constraints. It can be generalized for other constraint-based problems like Sudoku.
- Example LeetCode Problems:
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