(medium)LeetCode 241.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".

((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]

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

解法思想：递归

代码如下：

public class Solution {
    public List<Integer> diffWaysToCompute(String input) {
        List<Integer> ret=new LinkedList<Integer>();
        int len=input.length();
        for(int i=0;i<len;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> part1Ret=diffWaysToCompute(part1);
                   List<Integer> part2Ret=diffWaysToCompute(part2);
                   for(Integer p1:part1Ret){
                       for(Integer p2:part2Ret){
                           int c=0;
                           switch(input.charAt(i)){
                               case '+':c=p1+p2;
                                   break;
                               case '-':c=p1-p2;
                                   break;
                               case '*': c=p1*p2;
                           }
                           ret.add(c);
                       }
                   }
               }
        }
        if(ret.size()==0){
            ret.add(Integer.valueOf(input));
        }
        return ret;
    }
}

　　运行结果：