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Merged
merged 6 commits into from
Apr 1, 2023
Merged

[pull] main from doocs:main #506

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8acf35e
feat: add solutions to lc problem: No.1868
yanglbme Apr 1, 2023
38385f7
feat: add solutions to lc problem: No.0831
thinkasany Apr 1, 2023
304dc4d
feat: add solutions to lc problem: No.0439
yanglbme Apr 1, 2023
e25e85b
feat: add solutions to lc problem: No.1039
yanglbme Apr 1, 2023
be62e49
feat: add solutions to lc problem: No.0836
yanglbme Apr 1, 2023
a466920
feat: add solutions to lc problem: No.0851
yanglbme Apr 1, 2023
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131 changes: 130 additions & 1 deletion solution/0400-0499/0439.Ternary Expression Parser/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -55,22 +55,151 @@ or "(F ? 1 : (T ? 4 : 5))" --> "(T ? 4 : 5)" --> "4"

<!-- 这里可写通用的实现逻辑 -->

**方法一：栈**

我们从右到左遍历字符串 `expression`，对于当前遍历到的字符 $c$：

- 如果 $c$ 是字符 `':'`，则跳过；
- 如果 $c$ 是字符 `'?'`，那么意味着下一个即将遍历到的字符是条件表达式的条件，我们用一个布尔变量 `cond` 标记；
- 如果 $c$ 的上一个遍历到的字符是 `'?'`，也即布尔变量 `cond` 为 `true`，那么我们判断当前字符 $c$ 是否为字符 `'T'`，如果是，那么我们要保留栈顶第一个元素，弹出栈顶第二个元素；否则，我们要保留栈顶第二个元素，弹出栈顶第一个元素。最后，将 `cond` 置为 `false`；
- 否则，我们将当前字符 $c$ 入栈。

最后，栈中只剩下一个元素，即为表达式的结果。

时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 为字符串 `expression` 的长度。

<!-- tabs:start -->

### **Python3**

<!-- 这里可写当前语言的特殊实现逻辑 -->

```python

class Solution:
def parseTernary(self, expression: str) -> str:
stk = []
cond = False
for c in expression[::-1]:
if c == ':':
continue
if c == '?':
cond = True
else:
if cond:
if c == 'T':
x = stk.pop()
stk.pop()
stk.append(x)
else:
stk.pop()
cond = False
else:
stk.append(c)
return stk[0]
```

### **Java**

<!-- 这里可写当前语言的特殊实现逻辑 -->

```java
class Solution {
public String parseTernary(String expression) {
Deque<Character> stk = new ArrayDeque<>();
boolean cond = false;
for (int i = expression.length() - 1; i >= 0; --i) {
char c = expression.charAt(i);
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.pop();
stk.pop();
stk.push(x);
} else {
stk.pop();
}
cond = false;
} else {
stk.push(c);
}
}
}
return String.valueOf(stk.peek());
}
}
```

### **C++**

```cpp
class Solution {
public:
string parseTernary(string expression) {
string stk;
bool cond = false;
reverse(expression.begin(), expression.end());
for (char& c : expression) {
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.back();
stk.pop_back();
stk.pop_back();
stk.push_back(x);
} else {
stk.pop_back();
}
cond = false;
} else {
stk.push_back(c);
}
}
}
return {stk[0]};
}
};
```

### **Go**

```go
func parseTernary(expression string) string {
stk := []byte{}
cond := false
for i := len(expression) - 1; i >= 0; i-- {
c := expression[i]
if c == ':' {
continue
}
if c == '?' {
cond = true
} else {
if cond {
if c == 'T' {
x := stk[len(stk)-1]
stk = stk[:len(stk)-2]
stk = append(stk, x)
} else {
stk = stk[:len(stk)-1]
}
cond = false
} else {
stk = append(stk, c)
}
}
}
return string(stk[0])
}
```

### **...**
Expand Down
118 changes: 117 additions & 1 deletion solution/0400-0499/0439.Ternary Expression Parser/README_EN.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -55,13 +55,129 @@ or &quot;(F ? 1 : (T ? 4 : 5))&quot; --&gt; &quot;(T ? 4 : 5)&quot; --&gt; &quot
### **Python3**

```python

class Solution:
def parseTernary(self, expression: str) -> str:
stk = []
cond = False
for c in expression[::-1]:
if c == ':':
continue
if c == '?':
cond = True
else:
if cond:
if c == 'T':
x = stk.pop()
stk.pop()
stk.append(x)
else:
stk.pop()
cond = False
else:
stk.append(c)
return stk[0]
```

### **Java**

```java
class Solution {
public String parseTernary(String expression) {
Deque<Character> stk = new ArrayDeque<>();
boolean cond = false;
for (int i = expression.length() - 1; i >= 0; --i) {
char c = expression.charAt(i);
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.pop();
stk.pop();
stk.push(x);
} else {
stk.pop();
}
cond = false;
} else {
stk.push(c);
}
}
}
return String.valueOf(stk.peek());
}
}
```

### **C++**

```cpp
class Solution {
public:
string parseTernary(string expression) {
string stk;
bool cond = false;
reverse(expression.begin(), expression.end());
for (char& c : expression) {
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.back();
stk.pop_back();
stk.pop_back();
stk.push_back(x);
} else {
stk.pop_back();
}
cond = false;
} else {
stk.push_back(c);
}
}
}
return {stk[0]};
}
};
```

### **Go**

```go
func parseTernary(expression string) string {
stk := []byte{}
cond := false
for i := len(expression) - 1; i >= 0; i-- {
c := expression[i]
if c == ':' {
continue
}
if c == '?' {
cond = true
} else {
if cond {
if c == 'T' {
x := stk[len(stk)-1]
stk = stk[:len(stk)-2]
stk = append(stk, x)
} else {
stk = stk[:len(stk)-1]
}
cond = false
} else {
stk = append(stk, c)
}
}
}
return string(stk[0])
}
```

### **...**
Expand Down
31 changes: 31 additions & 0 deletions solution/0400-0499/0439.Ternary Expression Parser/Solution.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
class Solution {
public:
string parseTernary(string expression) {
string stk;
bool cond = false;
reverse(expression.begin(), expression.end());
for (char& c : expression) {
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.back();
stk.pop_back();
stk.pop_back();
stk.push_back(x);
} else {
stk.pop_back();
}
cond = false;
} else {
stk.push_back(c);
}
}
}
return {stk[0]};
}
};
27 changes: 27 additions & 0 deletions solution/0400-0499/0439.Ternary Expression Parser/Solution.go
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
func parseTernary(expression string) string {
stk := []byte{}
cond := false
for i := len(expression) - 1; i >= 0; i-- {
c := expression[i]
if c == ':' {
continue
}
if c == '?' {
cond = true
} else {
if cond {
if c == 'T' {
x := stk[len(stk)-1]
stk = stk[:len(stk)-2]
stk = append(stk, x)
} else {
stk = stk[:len(stk)-1]
}
cond = false
} else {
stk = append(stk, c)
}
}
}
return string(stk[0])
}
29 changes: 29 additions & 0 deletions solution/0400-0499/0439.Ternary Expression Parser/Solution.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
class Solution {
public String parseTernary(String expression) {
Deque<Character> stk = new ArrayDeque<>();
boolean cond = false;
for (int i = expression.length() - 1; i >= 0; --i) {
char c = expression.charAt(i);
if (c == ':') {
continue;
}
if (c == '?') {
cond = true;
} else {
if (cond) {
if (c == 'T') {
char x = stk.pop();
stk.pop();
stk.push(x);
} else {
stk.pop();
}
cond = false;
} else {
stk.push(c);
}
}
}
return String.valueOf(stk.peek());
}
}
21 changes: 21 additions & 0 deletions solution/0400-0499/0439.Ternary Expression Parser/Solution.py
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
class Solution:
def parseTernary(self, expression: str) -> str:
stk = []
cond = False
for c in expression[::-1]:
if c == ':':
continue
if c == '?':
cond = True
else:
if cond:
if c == 'T':
x = stk.pop()
stk.pop()
stk.append(x)
else:
stk.pop()
cond = False
else:
stk.append(c)
return stk[0]
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