1. Excel Sheet Column Number
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public int titleToNumber(String s) {
        int res = 0;
        for (int i = 0; i < s.length(); ++i) {
            res = res*26 + (s.charAt(i) - 'A' + 1);
        }
        return res;
    }

注意 res = 26 * res + (xxx)迭代res对应的s的顺序, 正反不要弄反了