Code02_DecodeString.java

package class039;

// 含有嵌套的字符串解码
// 测试链接 : https://leetcode.cn/problems/decode-string/
public class Code02_DecodeString {

	public static String decodeString(String str) {
		where = 0;
		return f(str.toCharArray(), 0);
	}

	public static int where;

	// s[i....]开始计算，遇到字符串终止 或者 遇到 ] 停止
	// 返回 : 自己负责的这一段字符串的结果
	// 返回之间，更新全局变量where，为了上游函数知道从哪继续！
	public static String f(char[] s, int i) {
		StringBuilder path = new StringBuilder();
		int cnt = 0;
		while (i < s.length && s[i] != ']') {
			if ((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z')) {
				path.append(s[i++]);
			} else if (s[i] >= '0' && s[i] <= '9') {
				cnt = cnt * 10 + s[i++] - '0';
			} else {
				// 遇到 [ 
				// cnt = 7 * ? 
				path.append(get(cnt, f(s, i + 1)));
				i = where + 1;
				cnt = 0;
			}
		}
		where = i;
		return path.toString();
	}

	public static String get(int cnt, String str) {
		StringBuilder builder = new StringBuilder();
		for (int i = 0; i < cnt; i++) {
			builder.append(str);
		}
		return builder.toString();
	}

}