剑指 Offer 58 - II. 左旋转字符串

Substring

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class Solution {
    public String reverseLeftWords(String s, int n) {
        return s.substring(n) + s.substring(0, n);
    }
}

Iterate

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class Solution {
    public String reverseLeftWords(String s, int n) {
        char[] chars = new char[s.length()];
        int j = 0;
        for (int i = n; i < s.length(); i++) {
            chars[j++] = s.charAt(i);
        }
        for (int i = 0; i < n; i++) {
            chars[j++] = s.charAt(i);
        }
        return new String(chars);
    }
}

References

剑指 Offer 58 - II. 左旋转字符串