How hard is LeetCode 241. Different Ways to Add Parentheses?

LeetCode 241. Different Ways to Add Parentheses is rated Medium on LeetCode.

What topics does LeetCode 241. Different Ways to Add Parentheses cover?

LeetCode 241. Different Ways to Add Parentheses is tagged Recursion, Memoization, Math, String and Dynamic Programming on LeetCode.

Different Ways to Add Parentheses — LeetCode 241 Python Solution

MediumRecursionMemoizationMathStringDynamic Programming

Problem: #241
Pattern: Dynamic Programming
Reading time: 4 min
Source: leetcode.com

The problem

Given a string expression of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order.

Example

Input: expression = "2-1-1"
Output: [0,2]
Explanation: ((2-1)-1) = 0

Python solution

Python

class Solution:
    def diffWaysToCompute(self, expression: str) -> List[int]:
        @cache
        def dfs(exp):
            if exp.isdigit():
                return [int(exp)]
            ans = []
            for i, c in enumerate(exp):
                if c in '-+*':
                    left, right = dfs(exp[:i]), dfs(exp[i + 1 :])
                    for a in left:
                        for b in right:
                            if c == '-':
                                ans.append(a - b)
                            elif c == '+':
                                ans.append(a + b)
                            else:
                                ans.append(a * b)
            return ans

        return dfs(expression)

Complexity

Measure	Complexity
Time	O(n·m) (typical)
Space	O(n·m) or optimized auxiliary

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 241. Different Ways to Add Parentheses is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Dynamic Programming and Memoization.

The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 241. Different Ways to Add Parentheses?: LeetCode 241. Different Ways to Add Parentheses is rated Medium on LeetCode.
What topics does LeetCode 241. Different Ways to Add Parentheses cover?: LeetCode 241. Different Ways to Add Parentheses is tagged Recursion, Memoization, Math, String and Dynamic Programming on LeetCode.