stack实现括号匹配
1.通过String类的内置函数置空string
public static boolean isValidByIf(String s){
while (s.contains("{}")||s.contains("[]")||s.contains("()")){
s=s.replace("{}","");
s=s.replace("[]","");
s=s.replace("()","");
}
return s.isEmpty();
}
2.通过stack实现
public static boolean isValidByStack(String s) {
Stack<Character> stack = new Stack<>();
char[] ch = s.toCharArray();
for (int i = 0; i < ch.length; i++) {//遍历字符数组，是左括号入栈
if (ch[i] == '(' || ch[i] == '[' || ch[i] == '{') {
stack.push(ch[i]);
} else {
// 右括号
if (stack.isEmpty()) return false;//stack为空不存在左括号，只有右括号所有无效
// 弹出栈顶元素
Character left = stack.pop();
if (left == '(' && ch[i] != ')') return false;
if (left == '{' && ch[i] != '}') return false;
if (left == '[' && ch[i] != ']') return false;
}
}
// stack为空，则括号匹配，有效，否则不为空，无效
return stack.isEmpty();
}
3.通过hashmap键值对的形式实现
public static boolean isValidByHM(String s) {
Stack<Character> stack = new Stack<>();
char[] ch = s.toCharArray();
for (int i = 0; i < ch.length; i++) {//遍历字符数组，是左括号入栈
if (hashMap.containsKey(ch[i])) {
stack.push(ch[i]);
} else {
// 右括号
if (stack.isEmpty()) return false;//stack为空不存在左括号，只有右括号所有无效
// 弹出栈顶元素
Character left = stack.pop();
// hashMap.get(left)根据栈弹出的left左括号get取值为对应的右括号，而ch[i]为右括号，不等则false
if (ch[i]!=hashMap.get(left)) return false;
}
}
// stack为空，则括号匹配，有效，否则不为空，无效
return stack.isEmpty();
}