CPP/stack_1.cpp at main · alwinimaginer/CPP · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
/*                                                        LEET CODE
Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.


Example 1:

Input: s = "()"

Output: true

Example 2:

Input: s = "()[]{}"

Output: true

Example 3:

Input: s = "(]"

Output: false

Example 4:

Input: s = "([])"

Output: true

Example 5:

Input: s = "([)]"

Output: false


Constraints:

1 <= s.length <= 104
s consists of parentheses only '()[]{}'.
*/

class Solution {
public:
    bool isValid(string s) {
        stack<char> st;

        for(char ch : s){
            if(ch == '(' || ch == '{' || ch == '['){
                 st.push(ch);
            }
            else if(ch == ')' || ch == '}' || ch == ']'){
                if(st.empty()) return false;

                char c = st.top();
                st.pop();

                if(c == '(' && ch != ')' ||
                   c == '{' && ch != '}' ||
                   c == '[' && ch != ']'){
                    return false;
                   }
            }
        }
        return st.empty();
    }
};