CS-Notes/docs/notes/Leetcode 题解 - 分治.md

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* [1. 给表达式加括号](#1-给表达式加括号)
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# 1. 给表达式加括号

[241. Different Ways to Add Parentheses (Medium)](https://leetcode.com/problems/different-ways-to-add-parentheses/description/)

```html
Input: "2-1-1".

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

Output : [0, 2]
```

```java
public List<Integer> diffWaysToCompute(String input) {
    List<Integer> ways = new ArrayList<>();
    for (int i = 0; i < input.length(); i++) {
        char c = input.charAt(i);
        if (c == '+' || c == '-' || c == '*') {
            List<Integer> left = diffWaysToCompute(input.substring(0, i));
            List<Integer> right = diffWaysToCompute(input.substring(i + 1));
            for (int l : left) {
                for (int r : right) {
                    switch (c) {
                        case '+':
                            ways.add(l + r);
                            break;
                        case '-':
                            ways.add(l - r);
                            break;
                        case '*':
                            ways.add(l * r);
                            break;
                    }
                }
            }
        }
    }
    if (ways.size() == 0) {
        ways.add(Integer.valueOf(input));
    }
    return ways;
}
```