26进制转换（A-Z：0-26；AA-AZ:27-52）

.java

  //----------------------26进制转换-----------------------
    @Test
    public void test14() {
        String str = "QQ";
        char[] chars = str.toCharArray();
        int sum = 0,index=0;
        for (int i = chars.length-1; i >=0 ; i--) {
            sum += Math.pow(26, index++) * (chars[i] - 64) ;
        }
        System.out.println(sum);
    }
    /**
     * a-z:97-122
     * A-Z:65-90
     */
    @Test
    public void convertToExcel(){
        int s = 459;
        int i = s / 26;
        StringBuilder stringBuilder = new StringBuilder();
        if (i != 0) {
            stringBuilder.append((char) (i + 'A'-1));
        }
        i = s % 26;
        if (i == 0) {
            stringBuilder.append('Z');
        } else {
            stringBuilder.append((char) (i + 'A'-1));
        }
        System.out.println(stringBuilder.toString());
    }