LeetCode - 20 - Valid Parentheses
2017-07-19 09:45
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Given a string containing just the characters
determine if the input string is valid.
The brackets must close in the correct order,
all valid but
not.
利用栈模拟,时间复杂度O(n),空间复杂度O(n)
'(',
')',
'{',
'}',
'['and
']',
determine if the input string is valid.
The brackets must close in the correct order,
"()"and
"()[]{}"are
all valid but
"(]"and
"([)]"are
not.
利用栈模拟,时间复杂度O(n),空间复杂度O(n)
class Solution { public: bool isValid(string s) { stack<char> ans; if (s == "" || s.length() % 2) return false; for (int i = 0; i < s.length(); ++i) { switch (s[i]) { case '(': case '{': case '[': ans.push(s[i]); break; case ')': if (ans.empty()) return false; if (ans.top() == '(') ans.pop(); else ans.push(s[i]); break; case '}': if (ans.empty()) return false; if (ans.top() == '{') ans.pop(); else ans.push(s[i]); break; case ']': if (ans.empty()) return false; if (ans.top() == '[') ans.pop(); else ans.push(s[i]); break; } } if (ans.empty()) return true; return false; } };
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