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Leetcode[241] Different Ways to Add Parentheses

29 Nov 2015

###Task1 Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are +, - and *.

Example 1
Input: "2-1-1".

((2-1)-1) = 0
(2-(1-1)) = 2
Output: [0, 2]


Example 2
Input: "2*3-4*5"

(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10
Output: [-34, -14, -10, -10, 10]

###Python

class Solution(object):
    def diffWaysToCompute(self, input):
        """
        :type input: str
        :rtype: List[int]
        """
        ret = []
        operators = ['+', '-', '*', '/']
        for i in range(len(input)):
            if input[i].isdigit():
                continue
            elif input[i] in operators:
                op = input[i]
                first = self.diffWaysToCompute(input[:i])
                second = self.diffWaysToCompute(input[i + 1:])
                for f in first:
                    for s in second:
                        ret.append(self.compute(f, s, op))
        if len(ret) == 0:
            return [int(input)]
        return ret
        
    def compute(self, f, s, op):
        map = { '+' : lambda f, s: f + s,
                '-' : lambda f, s: f - s,
                '*' : lambda f, s: f * s,
                '/' : lambda f, s: f * 1.0 / s
            }
        return map[op](f, s)

###Java

public class Solution {
    
    public int compute(int a, int b, char op) {
        switch (op) {
            case '+' :
                return a + b;
            case '-' :
                return a - b;
            case '*' :
                return a * b;
            default:
                break;
        }
        return 0;
    }
    
    public boolean isOperator(char op) {
        return (op == '+') || (op == '-') || (op == '*');
    }
    
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> res = new ArrayList<Integer>();
        if (input == null || input.length() == 0) {
            return res;
        }
        for (int i = 0; i < input.length(); i++) {
            char op = input.charAt(i);
            if (!isOperator(op)) {
                continue;
            }
            List<Integer> left = diffWaysToCompute(input.substring(0, i));
            List<Integer> right = diffWaysToCompute(input.substring(i + 1));
            for (int a: left) {
                for (int b: right) {
                    int val = compute(a, b, op);
                    res.add(val);
                }
            }
        }
        if (res.size() == 0) {
            res.add(Integer.parseInt(input));
        }
        return res;
    }
}

###Points

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