java.util包中提供了stack這個類,可以利用堆疊解決很多問題,比如經典的括號匹配問題

先看看stack這個類 
 
方法 

例題:

描述
現在，有一行括號序列，請你檢查這行括號是否配對。
輸入
第一行輸入一個數N（N 0-100）,表示有N組測試資料。後面的N行輸入多組輸入資料，每組輸入資料都是一個字串S(S的長度小於10000，且S不是空串），測試資料組數少於5組。資料保證S中只含有"[","]","(",")"四種字元
輸出
每組輸入資料的輸出佔一行，如果該字串中所含的括號是配對的，則輸出Yes,如果不配對則輸出No
樣例輸入

3
[(])
(])
([[]()])
樣例輸出
No
No
Yes

思路: 
當匹配到左括號則壓棧 
匹配到右括號,則和棧頂元素比較,匹配一對則出棧,否則返回No,結束判斷 
棧空還沒匹配完,也返回No,結束判斷

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">package</span> com.day1;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.util.Scanner;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> java.util.Stack;

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Main</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {
        Scanner input = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Scanner(System.in);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> n = input.nextInt();
        String[] arr = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> String[n];
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < arr.length; i++) {
            arr[i] = input.next();
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (String string : arr) {
            System.out.println(isMatch(string));
        }
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> String <span class="hljs-title" style="box-sizing: border-box;">isMatch</span>(String str){
        Stack<Character> stack = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Stack<>();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//建立棧</span>
        <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
         * 對字串逐個掃描
         * 遇到左括號入棧,遇到右括號則判斷
         */</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < str.length(); i++) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (str.charAt(i)!=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">')'</span> && str.charAt(i)!=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">']'</span>) {
                stack.push(str.charAt(i));
            }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">///棧空或者不匹配,則返回No</span>
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (stack.empty() || !isBracketMatch(stack.peek(), str.charAt(i))) {
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"No"</span>;
                }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
                    stack.pop();
                }
            }
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Yes"</span>;
    }
    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 判斷兩個括號是否匹配
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> c1
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> c2
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @return</span>
     */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">isBracketMatch</span>(Character c1,Character c2){
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (c1 == <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'('</span> && c2 == <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">')'</span>) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (c1 ==<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'['</span> && c2 ==<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">']'</span>) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;
    }
}</code>