102 lines
2 KiB
Markdown
102 lines
2 KiB
Markdown
# Leetcode Valid-Parentheses
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#### 2022-06-16 14:50
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> ##### Data structures:
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> #DS #stack
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> ##### Difficulty:
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> #coding_problem #difficulty-easy
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> ##### Additional tags:
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> #leetcode
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> ##### Revisions:
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> Initial encounter: 2022-06-16
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##### Related topics:
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```expander
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tag:#stack
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```
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##### Links:
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- [Link to problem](https://leetcode.com/problems/valid-parentheses/)
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___
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### Problem
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Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.
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An input string is valid if:
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1. Open brackets must be closed by the same type of brackets.
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2. Open brackets must be closed in the correct order.
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#### Examples
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**Example 1:**
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```markdown
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**Input:** s = "()"
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**Output:** true
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```
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**Example 2:**
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```markdown
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**Input:** s = "()[]{}"
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**Output:** true
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```
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**Example 3:**
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```markdown
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**Input:** s = "(]"
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**Output:** false
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```
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#### Constraints
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- `1 <= s.length <= 104`
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- `s` consists of parentheses only `'()[]{}'`.
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### Thoughts
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Basic stack usage.
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Can be implemented using std_stack or stc_vector.
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obviously i should use std_stack.
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### Solution
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```cpp
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class Solution {
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public:
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bool isValid(string s) {
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vector<char> stack;
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vector<vector<char>> pairs = {{'(', ')'}, {'{', '}'}, {'[', ']'}};
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int loc;
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const int size = pairs.size();
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for (char c : s) {
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for (loc = 0; loc < size; loc++) {
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if (c == pairs[loc][1]) {
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if (stack.empty()) {
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// if there is no {([ before
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printf("No {([ before.\n");
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return false;
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} else if (stack.back() == pairs[loc][0]) {
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stack.pop_back();
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} else {
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// parens mismatch
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printf("parens mismatch: %c %c\n", stack.back(), pairs[loc][0]);
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return false;
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}
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} else if (c == pairs[loc][0]) {
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stack.push_back(c);
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}
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}
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}
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if (stack.empty()) {
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return true;
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} else {
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return false;
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}
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}
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};
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``` |