Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Sign up
Appearance settings

Commit fa467e6

Browse files
feat: add solutions to lcof2 problem: No.036 Evaluate Reverse Polish Notation
1 parent f3663ff commit fa467e6

File tree

5 files changed

+203
-1
lines changed

5 files changed

+203
-1
lines changed

‎lcof2/剑指 Offer II 036. 后缀表达式/README.md‎

Lines changed: 108 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -86,22 +86,129 @@
8686

8787
<!-- 这里可写通用的实现逻辑 -->
8888

89+
利用栈存储运算数,每次遇到符号,对栈顶两个元素进行运算
90+
8991
<!-- tabs:start -->
9092

9193
### **Python3**
9294

9395
<!-- 这里可写当前语言的特殊实现逻辑 -->
9496

95-
```python
97+
需要注意 Python 的整除对负数也是向下取整(例如:`6 // -132 = -1`),和答案对应不上,所以需要特殊处理
9698

99+
```python
100+
class Solution:
101+
def evalRPN(self, tokens: List[str]) -> int:
102+
nums = []
103+
for t in tokens:
104+
if len(t) > 1 or t.isdigit():
105+
nums.append(int(t))
106+
else:
107+
if t == "+":
108+
nums[-2] += nums[-1]
109+
elif t == "-":
110+
nums[-2] -= nums[-1]
111+
elif t == "*":
112+
nums[-2] *= nums[-1]
113+
else:
114+
nums[-2] = int(nums[-2] / nums[-1])
115+
nums.pop()
116+
return nums[0]
97117
```
98118

99119
### **Java**
100120

101121
<!-- 这里可写当前语言的特殊实现逻辑 -->
102122

103123
```java
124+
class Solution {
125+
public int evalRPN(String[] tokens) {
126+
Deque<Integer> stack = new ArrayDeque<>();
127+
for (String t : tokens) {
128+
if (t.length() > 1 || Character.isDigit(t.charAt(0))) {
129+
stack.push(Integer.parseInt(t));
130+
} else {
131+
int y = stack.pop();
132+
int x = stack.pop();
133+
switch (t) {
134+
case "+":
135+
stack.push(x + y);
136+
break;
137+
case "-":
138+
stack.push(x - y);
139+
break;
140+
case "*":
141+
stack.push(x * y);
142+
break;
143+
default:
144+
stack.push(x / y);
145+
break;
146+
}
147+
}
148+
}
149+
return stack.pop();
150+
}
151+
}
152+
```
153+
154+
### **Go**
155+
156+
```go
157+
func evalRPN(tokens []string) int {
158+
// https://github.com/emirpasic/gods#arraystack
159+
stack := arraystack.New()
160+
for _, token := range tokens {
161+
if len(token) > 1 || token[0] >= '0' && token[0] <= '9' {
162+
num, _ := strconv.Atoi(token)
163+
stack.Push(num)
164+
} else {
165+
y := popInt(stack)
166+
x := popInt(stack)
167+
switch token {
168+
case "+":
169+
stack.Push(x + y)
170+
case "-":
171+
stack.Push(x - y)
172+
case "*":
173+
stack.Push(x * y)
174+
default:
175+
stack.Push(x / y)
176+
}
177+
}
178+
}
179+
return popInt(stack)
180+
}
181+
182+
func popInt(stack *arraystack.Stack) int {
183+
v, _ := stack.Pop()
184+
return v.(int)
185+
}
186+
```
104187

188+
### **C++**
189+
190+
```cpp
191+
class Solution {
192+
public:
193+
int evalRPN(vector<string>& tokens) {
194+
stack<int> stk;
195+
for (const auto& token : tokens) {
196+
if (token.size() > 1 || isdigit(token[0])) {
197+
stk.push(stoi(token));
198+
} else {
199+
int y = stk.top();
200+
stk.pop();
201+
int x = stk.top();
202+
stk.pop();
203+
if (token[0] == '+') stk.push(x + y);
204+
else if (token[0] == '-') stk.push(x - y);
205+
else if (token[0] == '*') stk.push(x * y);
206+
else stk.push(x / y);
207+
}
208+
}
209+
return stk.top();
210+
}
211+
};
105212
```
106213
107214
### **...**
Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
class Solution {
2+
public:
3+
int evalRPN(vector<string>& tokens) {
4+
stack<int> stk;
5+
for (const auto& token : tokens) {
6+
if (token.size() > 1 || isdigit(token[0])) {
7+
stk.push(stoi(token));
8+
} else {
9+
int y = stk.top();
10+
stk.pop();
11+
int x = stk.top();
12+
stk.pop();
13+
if (token[0] == '+') stk.push(x + y);
14+
else if (token[0] == '-') stk.push(x - y);
15+
else if (token[0] == '*') stk.push(x * y);
16+
else stk.push(x / y);
17+
}
18+
}
19+
return stk.top();
20+
}
21+
};
Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,29 @@
1+
func evalRPN(tokens []string) int {
2+
// https://github.com/emirpasic/gods#arraystack
3+
stack := arraystack.New()
4+
for _, token := range tokens {
5+
if len(token) > 1 || token[0] >= '0' && token[0] <= '9' {
6+
num, _ := strconv.Atoi(token)
7+
stack.Push(num)
8+
} else {
9+
y := popInt(stack)
10+
x := popInt(stack)
11+
switch token {
12+
case "+":
13+
stack.Push(x + y)
14+
case "-":
15+
stack.Push(x - y)
16+
case "*":
17+
stack.Push(x * y)
18+
default:
19+
stack.Push(x / y)
20+
}
21+
}
22+
}
23+
return popInt(stack)
24+
}
25+
26+
func popInt(stack *arraystack.Stack) int {
27+
v, _ := stack.Pop()
28+
return v.(int)
29+
}
Lines changed: 28 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,28 @@
1+
class Solution {
2+
public int evalRPN(String[] tokens) {
3+
Deque<Integer> stack = new ArrayDeque<>();
4+
for (String t : tokens) {
5+
if (t.length() > 1 || Character.isDigit(t.charAt(0))) {
6+
stack.push(Integer.parseInt(t));
7+
} else {
8+
int y = stack.pop();
9+
int x = stack.pop();
10+
switch (t) {
11+
case "+":
12+
stack.push(x + y);
13+
break;
14+
case "-":
15+
stack.push(x - y);
16+
break;
17+
case "*":
18+
stack.push(x * y);
19+
break;
20+
default:
21+
stack.push(x / y);
22+
break;
23+
}
24+
}
25+
}
26+
return stack.pop();
27+
}
28+
}
Lines changed: 17 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,17 @@
1+
class Solution:
2+
def evalRPN(self, tokens: List[str]) -> int:
3+
nums = []
4+
for t in tokens:
5+
if len(t) > 1 or t.isdigit():
6+
nums.append(int(t))
7+
else:
8+
if t == "+":
9+
nums[-2] += nums[-1]
10+
elif t == "-":
11+
nums[-2] -= nums[-1]
12+
elif t == "*":
13+
nums[-2] *= nums[-1]
14+
else:
15+
nums[-2] = int(nums[-2] / nums[-1])
16+
nums.pop()
17+
return nums[0]

0 commit comments

Comments
(0)

AltStyle によって変換されたページ (->オリジナル) /