LeetCode: Different Ways to Add Parentheses

LeetCode: Different Ways to Add Parentheses

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".

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((2-1)-1) = 0
(2-(1-1)) = 2

Output: [0, 2]

Example 2

Input: "2*3-4*5"

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(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]

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public class Solution {
public List<Integer> diffWaysToCompute(String input) {
List<Integer> result = new ArrayList<>();

if (input == null || input.length() == 0) {
return result;
}

for (int i = 0; i < input.length(); i++) {
char c = input.charAt(i);
if (!isOperator(c)) {
continue;
}

List<Integer> p1 = diffWaysToCompute(input.substring(0, i));
List<Integer> p2 = diffWaysToCompute(input.substring(i + 1, input.length()));

for (int a : p1) {
for (int b : p2) {
result.add(calc(a, b, c));
}
}
}
// if input is a single number
if (result.isEmpty()) {
result.add(Integer.parseInt(input));
}

return result;
}

private boolean isOperator(char c) {
return c == '+' || c == '-' || c == '*';
}

private int calc(int a, int b, char c) {
switch (c) {
case '+':
return a + b;
case '-':
return a - b;
case '*':
return a * b;
//default should never be reached
default:
return Integer.MAX_VALUE;
}
}
}