LongestValidParentheses, 求最长合法括号子串长度-----同类问题ValidParentheses，GenerateParentheses

public static int longestValidParentheses(String s) {
Stack<int[]> stack = new Stack<int[]>();
int result = 0;

for(int i=0; i<=s.length()-1; i++)
{
char c = s.charAt(i);
if(c=='(')//如果是左括号
{
int[] a = {i,0};
stack.push(a);
}
else//如果是右括号
{
if(stack.empty()||stack.peek()[1]==1)//如果栈为空或者栈顶元素为右括号
{
int[] a = {i,1};
stack.push(a);
}
else
{
stack.pop();
int currentLen=0;
if(stack.empty())
{
currentLen = i+1;
}
else
{
currentLen = i-stack.peek()[0];
}
result = Math.max(result, currentLen);
}
}
}

return result;
}