Given an equation, represented by `words` on the left side and the `result` on the right side.

You need to check if the equation is solvable under the following rules:

- Each character is decoded as one digit (0 - 9).
- Every pair of different characters must map to different digits.
- Each `words[i]` and `result` are decoded as one number without leading zeros.
- Sum of numbers on the left side (`words`) will equal to the number on the right side (`result`).

Return `true` if the equation is solvable, otherwise return `false`.

Example 1:

    Input: words = ["SEND","MORE"], result = "MONEY"
    Output: true
    Explanation: Map 'S'-> 9, 'E'->5, 'N'->6, 'D'->7, 'M'->1, 'O'->0, 'R'->8, 'Y'->'2'
    Such that: "SEND" + "MORE" = "MONEY" ,  9567 + 1085 = 10652

Example 2:

    Input: words = ["SIX","SEVEN","SEVEN"], result = "TWENTY"
    Output: true
    Explanation: Map 'S'-> 6, 'I'->5, 'X'->0, 'E'->8, 'V'->7, 'N'->2, 'T'->1, 'W'->'3', 'Y'->4
    Such that: "SIX" + "SEVEN" + "SEVEN" = "TWENTY" ,  650 + 68782 + 68782 = 138214

Example 3:

    Input: words = ["LEET","CODE"], result = "POINT"
    Output: false

Constraints:

- `2 <= words.length <= 5`
- `1 <= words[i].length, result.length <= 7`
- `words[i], result` contain only uppercase English letters.
- The number of different characters used in the expression is at most `10`.