> For the complete documentation index, see [llms.txt](https://m0uk4.gitbook.io/notebooks/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://m0uk4.gitbook.io/notebooks/mouka/algorithms/greedy/shi-kuo-hao-ping-heng-de-zui-xiao-jiao-huan-ci-shu.md).

# 使括号平衡的最小交换次数

### 描述：

给定 2N 长度的字符串，包含N个 '\[' ，N个 ']'，计算使字符串平衡的最小交换次数

平衡字符串定义：S1\[S2]， 其中 S1，S2均为平衡字符串

### 输入： 

2N长度字符串

### 输出：

最小交换次数

### 举例：

> Input : \[]]\[]\[ 
>
> Output : 2 
>
> First swap: Position 3 and 4 \[]\[]]\[ 
>
> Second swap: Position 5 and 6 \[]\[]\[]
>
> Input : \[\[]\[]] 
>
> Output : 0 
>
> String is already balanced.

{% hint style="info" %}
Solution is below
{% endhint %}

### 思路

顺序遍历字符串，当遇到不匹配的']'时（遇到相应的'\['之前），将其与之后最接近它的']'交换位置

### 实现

{% tabs %}
{% tab title="Python" %}

```python
def MinSwapBracketBalancing(Brackets: list):
	# 首先遍历字符串，获取所有左括号的位置
	leftBrackets = []
	leftBrackets.extend([ idx for idx, x in enumerate(Brackets) if x == '['])

	if len(leftBrackets) != len(Brackets) // 2:	
		return 0

	count = 0	# 当前还未平衡的左括号数量
	pos = 0		# 下一个左括号的位置
	sum = 0		# 总共移动次数

	i = 0
	while i < len(Brackets):
		if Brackets[i] == '[':
			# 当前遍历括号为左括号
			count += 1
			pos += 1
		else:
			# 当前括号为右括号
			count -= 1	# 不平衡左括号 - 1
			if count < 0:
				# 右括号在不平衡左括号之前出现
				# 交换两括号位置
				Brackets[i], Brackets[leftBrackets[pos]] = Brackets[leftBrackets[pos]],Brackets[i]

				sum += leftBrackets[pos] - i
				count = 0
				pos += 1
				i += 1
		i += 1

	return sum
```

{% endtab %}

{% tab title="C++" %}

```cpp
int MinSwapsBracketBalancing(string Brackets) {
	vector<int> leftBrackets;

	// Get positions of all left brackets
	for (auto i = 0;i<Brackets.size(); i++) {
		if (Brackets[i] == '[')
			leftBrackets.push_back(i);
	}

	auto count = 0;	// Current unbalanced left brackets
	auto pos = 0;	// Next position of next left brackets
	auto sum = 0;	// Total moves to balance brackets

	for (auto i = 0; i < Brackets.size(); i++) {
		if (Brackets[i] == '[') {
			count++;
			pos++;
		}
		else if (--count < 0) {
			// Get unbalanced right bracket
			// Swap it with next left bracket
			swap(Brackets[i], Brackets[leftBrackets[pos]]);
			sum += leftBrackets[pos] - i;
		}
	}

	return sum;

}
```

{% endtab %}
{% endtabs %}

```python
```