44 lines
1.2 KiB
C++
44 lines
1.2 KiB
C++
#include <algorithm>
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#include <stack>
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class Solution {
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public:
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int longestValidParentheses(string s) {
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int len = s.size();
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int maxp = 0;
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stack<int> stk;
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for (int i = 0; i < len; i++)
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{
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if (s[i] == '(')
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{
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stk.push(i);
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}
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else // if (s[i] == ')')
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{
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// Stack not empty, and symbol matches.
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if (!stk.empty() && s[stk.top()]=='(')
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{
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// Pop matched pairs.
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stk.pop();
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if (stk.empty())
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{
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// From Start to i is a valid string.
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maxp = std::max(i + 1, maxp);
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}
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else
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{
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// From stk.top()+1 to i is a valid string. Length: i-(stk.top()+1)+1
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maxp = std::max(i - stk.top(), maxp);
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}
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}
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else
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{
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// new start point (stub)
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stk.push(i);
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}
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}
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}
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return maxp;
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}
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};
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