LeetCode 46: Permutations — Step-by-Step Visual Trace

Medium — Backtracking | Array | Recursion The Problem Given an array of distinct integers, return all possible permutations of the array elements in any order. Approach Uses backtracking with in-place swapping to generate permutations. At each position, we try placing each remaining element, recursively generate permutations for the rest, then backtrack by swapping elements back to their original positions. Time: O(n! × n) · Space: O(n) Code class Solution : def permute ( self , nums : List [ int ]) -> List [ List [ int ]]: def backtrack ( start ): if start == len ( nums ) - 1 : permutations . append ( nums [:]) # Append a copy of the current permutation for i in range ( start , len ( nums )): nums [ start ], nums [ i ] = nums [ i ], nums [ start ] # Swap elements backtrack ( start + 1 ) nums [ start ], nums [ i ] = nums [ i ], nums [ start ] # Backtrack permutations = [] backtrack ( 0 ) return permutations Watch It Run Open interactive visualization Try it yourself: Open TraceLit and