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Given a string 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.
Note that an empty string is also considered valid.
Example 1:
Input: "()" Output: true
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]" Output: false
Example 4:
Input: "([)]" Output: false
Example 5:
Input: "{[]}"
Output: true
题目链接：https://leetcode.com/problems/valid-parentheses/
题目分析：栈模拟
class Solution {
public boolean isValid(String s) {
int top = 0;
int[] stk = new int[s.length() + 1];
for (int i = 0; i < s.length(); i++) {
char ch = s.charAt(i);
if (ch == '(' || ch == '[' || ch == '{') {
stk[++top] = ch;
} else if (ch == ')' && top > 0 && stk[top] == '(') {
top--;
} else if (ch == ']' && top > 0 && stk[top] == '[') {
top--;
} else if (ch == '}' && top > 0 && stk[top] == '{') {
top--;
} else {
return false;
}
}
return top == 0;
}
}