[LeetCode] 20. Valid Parentheses
2017-10-08 21:14
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题目:https://leetcode.com/problems/valid-parentheses/description/
determine if the input string is valid.
The brackets must close in the correct order,
all valid but
not.
1.栈的使用
声明:std::stack<char> stack;
操作:添加 stack.push();是否为空stack.empty();取top:stack.top();删除top:stack.pop();
2.switch-case
switch(char){
case 'a':{
cout<<char<<endl;
break;
}
}
1.栈的使用:
声明:
Stack<Character> chstack = new Stack<Character>();
其中<>中应为对象,而char为内置数据类型,所以需要使用 Character 类型,可以和char 用'=='比较,用'='赋值。
操作:
添加:chstack.push();
取top并删除:chstack.pop();
2.switch-case
switch(c){
case '{':
pass;
break;
default:
pass;
break;
}
题目
Given a string containing just the characters'(',
')',
'{',
'}',
'['and
']',
determine if the input string is valid.
The brackets must close in the correct order,
"()"and
"()[]{}"are
all valid but
"(]"and
"([)]"are
not.
思路
需要后进先出来做匹配,用栈非常合适。class Solution { public: bool isValid(string s) { std::stack<char> chstack; for(int i = 0 ;i<s.length();i++){ if(s[i]=='('||s[i]=='{'||s[i]=='[') chstack.push(s[i]); else{ if(chstack.empty()) return false; char chtmp = chstack.top(); chstack.pop(); switch(chtmp){ case '(':{ if(s[i]==')') continue; else return false; break; } case '{':{ if(s[i]=='}') continue; else return false; break; } case '[':{ if(s[i]==']') continue; else return false; break; } } } } if(!chstack.empty()) return false; return true; } };
1.栈的使用
声明:std::stack<char> stack;
操作:添加 stack.push();是否为空stack.empty();取top:stack.top();删除top:stack.pop();
2.switch-case
switch(char){
case 'a':{
cout<<char<<endl;
break;
}
}
JAVA
class Solution { public boolean isValid(String s) { Stack<Character> chstack = new Stack<Character>(); for(char c : s.toCharArray()){ if(c=='(') chstack.push(')'); else if(c=='{') chstack.push('}'); else if(c=='[') chstack.push(']'); else if(chstack.isEmpty()||chstack.pop()!=c) return false; } return chstack.isEmpty(); } }语法:
1.栈的使用:
声明:
Stack<Character> chstack = new Stack<Character>();
其中<>中应为对象,而char为内置数据类型,所以需要使用 Character 类型,可以和char 用'=='比较,用'='赋值。
操作:
添加:chstack.push();
取top并删除:chstack.pop();
class Solution { public boolean isValid(String s) { Stack<Character> chstack = new Stack<Character>(); for(char c : s.toCharArray()){ switch(c){ case '(': chstack.push(')'); break; case '{': chstack.push('}'); break; case '[': chstack.push(']'); break; default: if(chstack.isEmpty()||chstack.pop()!=c) return false; } } return chstack.isEmpty(); } }语法:
2.switch-case
switch(c){
case '{':
pass;
break;
default:
pass;
break;
}
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