每3日一篇leetcode，第五題：ZigZagConversion

1.一個字符串按照指定的行數用zigzag的格式排列起來，而後按行從左到右閱讀起來，成爲一個新的字符串

//13 ms	39.4 MB
    public String convert(String s, int numRows) {
        if (numRows == 1) {
            return s;
        }
        String[] strings1 = new String[numRows];
        for (int i = 0; i < numRows; i++) {
            strings1[i] = "";
        }
        int len = s.length();
        int per = 2 * numRows - 2;
        LinkedList<ArrayList<String>> ll = new LinkedList<>();
        ArrayList<String> arrayList = null;
        ArrayList<String> arrayList2 = null;
        for (int i = 0; i < len; i++) {
            int left = i % per;
            int left2 = left - numRows;
            int n = (left / numRows);
            if (left == 0) {
                arrayList = new ArrayList<>();
                ll.add(arrayList);
            }
            if (left2 == 0) {
                arrayList2 = new ArrayList<String>(Arrays.asList(strings1));
//                for (int j = 0; j < numRows; j++) {
//                    arrayList2.add("");
//                }
                ll.add(arrayList2);
            }


            if (n < 1) {
                arrayList.add(s.charAt(i) + "");
            } else if (n == 1 && arrayList2 != null) {
                arrayList2.set(numRows - 1 - 1 - left2, s.charAt(i) + "");
            }
        }

        StringBuilder stringBuilder = new StringBuilder();
        for (int m = 0; m < numRows; m++) {
            for (int n = 0, size = ll.size(); n < size; n++) {
                ArrayList<String> strings = ll.get(n);
                stringBuilder.append(m >= strings.size() ? "" : strings.get(m));
            }
        }
        return stringBuilder.toString();
    }
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