394. 字串解碼

package 字串;

import java.util.Stack;

public class 字串解碼 {
    public static void main(String[] args) {
        String s = "3[a2[c]]";
        字串解碼 o = new 字串解碼();
        String s1 = o.decodeString(s);
        System.out.println(s1);
    }


    // 利用棧找中括號的另一半，遇到中括號左邊就去找另一半
    // 將中括號裡面的字元複寫
    
 
// 反覆遞迴，直到字串中不含有左半邊中括號為止
    public String decodeString(String s) {
        if (!s.contains("[")) {
            return s;
        }
        char[] chars = s.toCharArray();
        int i = 0;
        while (chars[i] != '[' && i < chars.length) {
            i++;
        }
        int end = getNextIndex(chars, i);
        String s1 
 
= deCodeIndex(s, i, end);
        return decodeString(s1);
    }

    public int getNextIndex(char[] chars, int i) {
        Stack<Character> stack = new Stack<>();
        stack.push(chars[i]);
        int j = i + 1;
        while (!stack.isEmpty()) {
            if (chars[j] == '[') {
                stack.push(
 
'[');
            }
            if (chars[j] == ']') {
                stack.pop();
            }
            j++;
        }
        return --j;
    }

    public String deCodeIndex(String s, int start, int end) {
        String s1 = "";
        String s3 = s.substring(end + 1, s.length());
        String s2 = "";
        String k="";
        int numStart=-1;
        for (int i = 0; i < start; i++) {
            if(s.charAt(i)>='0' && s.charAt(i)<='9'){
                k+=String.valueOf(s.charAt(i));
                if(numStart==-1){
                    numStart=i;
                }
            }
        }
        if(numStart>0){
            s1 = s.substring(0, numStart);
        }

        int count=Integer.parseInt(k);
        for (int i = 0; i < count; i++) {
            s2 += s.substring(start + 1, end);
        }
        return s1 + s2 + s3;
    }
    
}

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