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Merged
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Oct 20, 2018
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Add Solution20[CPP] #34

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87 changes: 86 additions & 1 deletion solution/020.Valid Parentheses/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,10 @@
### 解法
遍历 string，遇到左括号，压入栈中；遇到右括号，从栈中弹出元素，元素不存在或者元素与该右括号不匹配，返回 false。遍历结束，栈为空则返回 true，否则返回 false。

```java
因为字符串只包含"(){}[]",也可以进行特殊处理，用映射来做

#### java
```
class Solution {
public boolean isValid(String s) {
if (s == null || s == "") {
Expand Down Expand Up @@ -80,4 +83,86 @@ class Solution {
return a == ')' || a == ']' || a == '}';
}
}
```

#### C++
```
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写代码块的时候，可以加上特定的语言噢，识别度较高~
e.g.

```cpp

code here...

```

```java

code here...

```


class Solution {
public:
bool isValid(string s) {
stack<char> _stack;
int len = s.length();
if(len == 0)return true;
char ch;
for(int i= 0;i<len;i++)
{
if(s[i] == '{' ||s[i] == '['||s[i] == '(' )
{
_stack.push(s[i]);
}
if(s[i] == '}')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '{')return false;
else _stack.pop();

}
else if(s[i] == ']')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '[')return false;
else _stack.pop();
}
else if(s[i] == ')')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '(')return false;
else _stack.pop();
}
}

if(!_stack.empty())return false;

return true;

}
};

//特殊
class Solution {
public:
bool isValid(string s) {
map<char,int> m={
{'[',1},
{']',-1},
{'{',2},
{'}',-2},
{'(',3},
{')',-3}
};
stack<int> sk;
for(int i=0;i<s.length();i++){
if(m[s[i]]<0 ){
if(!sk.empty() && sk.top()==(-m[s[i]])){
sk.pop();
}else{
return false;
}
}else{
sk.push(m[s[i]]);
}
}
if(sk.empty())
return true;
return false;
}
};

```
79 changes: 79 additions & 0 deletions solution/020.Valid Parentheses/Solution.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,79 @@
class Solution {
public:
bool isValid(string s) {
stack<char> _stack;
int len = s.length();
if(len == 0)return true;
char ch;
for(int i= 0;i<len;i++)
{
if(s[i] == '{' ||s[i] == '['||s[i] == '(' )
{
_stack.push(s[i]);
}
if(s[i] == '}')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '{')return false;
else _stack.pop();

}
else if(s[i] == ']')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '[')return false;
else _stack.pop();
}
else if(s[i] == ')')
{
if(_stack.empty())return false;
else ch = _stack.top();

if(ch != '(')return false;
else _stack.pop();
}
}

if(!_stack.empty())return false;

return true;

}
};



-----------------
//特殊
class Solution {
public:
bool isValid(string s) {
map<char,int> m={
{'[',1},
{']',-1},
{'{',2},
{'}',-2},
{'(',3},
{')',-3}
};
stack<int> sk;
for(int i=0;i<s.length();i++){
if(m[s[i]]<0 ){
if(!sk.empty() && sk.top()==(-m[s[i]])){
sk.pop();
}else{
return false;
}
}else{
sk.push(m[s[i]]);
}
}
if(sk.empty())
return true;
return false;
}
};