LeetCode 20. Valid Parentheses

https://leetcode.com/problems/valid-parentheses/description/

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.

字符串简单题 + 数据结构栈
注意针对')'的情况，需要判断栈是否为空。
扫描字符串时，用引用访问能节省时间。
stack - C++ Reference
- http://www.cplusplus.com/reference/stack/stack/

 1 //
 2 //  main.cpp
 3 //  LeetCode
 4 //
 5 //  Created by Hao on 2017/3/16.
 6 //  Copyright © 2017年 Hao. All rights reserved.
 7 //
 8 
 9 #include <iostream>
10 #include <stack>
11 #include <vector>
12 using namespace std;
13 
14 class Solution {
15 public:
16     bool isValid(string s) {
17         stack<char> sStack;
18         
19         for (char & ch : s) { // scan string with reference to save time
20             switch (ch) {
21                 case '(':
22                 case '[':
23                 case '{': sStack.push(ch);
24                           break;
25                 case ')': if (sStack.empty() || sStack.top() != '(') // pay attention to sStack.empty() for the case ')'
26                               return false;
27                           else {
28                               sStack.pop();
29                               break;
30                           }
31                 case ']': if (sStack.empty() || sStack.top() != '[')
32                               return false;
33                           else {
34                               sStack.pop();
35                               break;
36                           }
37                 case '}': if (sStack.empty() || sStack.top() != '{')
38                               return false;
39                           else {
40                               sStack.pop();
41                               break;
42                           }
43                 default: ;
44             }
45         }
46         
47         return sStack.empty(); // check if all parentheses are matched
48     }
49 };
50 
51 int main(int argc, char* argv[])
52 {
53     Solution    testSolution;
54     
55     vector<string> iVec = {"()", "()[]{}", "(]", "([)]", "]"};
56     bool result = true;
57 
58     result = result && testSolution.isValid(iVec[0]);
59     result = result && testSolution.isValid(iVec[1]);
60     result = result && ! testSolution.isValid(iVec[2]);
61     result = result && ! testSolution.isValid(iVec[3]);
62     result = result && ! testSolution.isValid(iVec[4]);
63 
64     if (result)
65         cout << "All tests pass!" << endl;
66     else
67         cout << "Not all tests pass!" << endl;
68     
69     return 0;
70 }

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posted on 2018-02-10 10:54 浩然119 阅读(126) 评论(0) 编辑收藏举报