1849. Splitting a String Into Descending Consecutive Values

Description

You are given a string s that consists of only digits.

Check if we can split s into two or more non-empty substrings such that the numerical values of the substrings are in descending order and the difference between numerical values of every two adjacent substrings is equal to 1.

• For example, the string s = "0090089" can be split into ["0090", "089"] with numerical values [90,89]. The values are in descending order and adjacent values differ by 1, so this way is valid.
• Another example, the string s = "001" can be split into ["0", "01"], ["00", "1"], or ["0", "0", "1"]. However all the ways are invalid because they have numerical values [0,1], [0,1], and [0,0,1] respectively, all of which are not in descending order.

Return true if it is possible to split s​​​​​​ as described above, or false otherwise.

A substring is a contiguous sequence of characters in a string.

 

Example 1:

Input: s = "1234"
Output: false
Explanation: There is no valid way to split s.

Example 2:

Input: s = "050043"
Output: true
Explanation: s can be split into ["05", "004", "3"] with numerical values [5,4,3].
The values are in descending order with adjacent values differing by 1.

Example 3:

Input: s = "9080701"
Output: false
Explanation: There is no valid way to split s.

 

Constraints:

• 1 <= s.length <= 20
• s only consists of digits.

 

Solutions

Solution: Backtracking

• Time complexity: O(n²)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string} s
 * @return {boolean}
 */
const splitString = function (s) {
  const size = s.length;
  const isValid = (start, target) => {
    for (let index = start; index < size; index++) {
      const value = +s.slice(start, index + 1);

      if (target - value !== 1) continue;
      if (index === size - 1) return true;
      if (isValid(index + 1, value)) return true;
    }
    return false;
  };

  for (let index = 0; index < size; index++) {
    const value = +s.slice(0, index + 1);

    if (isValid(index + 1, value)) return true;
  }
  return false;
};