Dsa Backtrack Subsets

In this tutorial, you'll learn about How to Fix Subsets Errors. We cover key concepts, practical examples, and best practices.

Fix subsets errors when state not properly copied or duplicate subsets generated.

Quick Fix

Wrong

def subsets(n):
    res=[[]]
    for x in n:
        for i in range(len(res)):
            res.append(res[i]+[x])
    return res

Iterative approach works but appending while iterating can confuse. Use list() copy.

Right

def subsets(n):
    res=[[]]
    for x in n:
        res+=[[x]+s for s in res]
    return res
# Or backtracking:
def subsets(n):
    res=[]
    def dfs(i,cur):
        if i==len(n): res.append(cur.copy()); return
        dfs(i+1,cur)  # skip
        cur.append(n[i]); dfs(i+1,cur); cur.pop()  # include
    dfs(0,[])
    return res

[1,2,3] -> [[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]. O(2^n).

Prevention

For each element: include or exclude. Backtrack or iterative accumulation.

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