[leetCode] Different Ways to Add Parentheses

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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]

public class Solution {    HashMap<String, List<Integer>> map;    public List<Integer> diffWaysToCompute(String input) {        map = new HashMap<String, List<Integer>>();        List<Integer> res = new ArrayList<Integer>();        for (int i = 0; i < input.length(); i++) {            if (input.charAt(i) == '+' ||                    input.charAt(i) == '-' ||                    input.charAt(i) == '*') {                String part1 = input.substring(0, i);                String part2 = input.substring(i+1);                List<Integer> op1 = map.get(part1);                List<Integer> op2 = map.get(part2);                if (op1 == null) {                    op1 = diffWaysToCompute(part1);                    map.put(part1, op1);                }                if (op2 == null) {                    op2 = diffWaysToCompute(part2);                    map.put(part2, op2);                }                for ( Integer n1 : op1) {                    for (Integer n2 : op2 ) {                        if (input.charAt(i) == '+') {                            res.add(n1 + n2);                        }                        if (input.charAt(i) == '-') {                            res.add(n1 - n2);                        }                        if (input.charAt(i) == '*') {                            res.add(n1 * n2);                        }                    }                }            }        }        if (res.isEmpty()) {            res.add(Integer.valueOf(input));        }        return res;    }}

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