Description.txt

Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.

Note:
The length of num is less than 10002 and will be ≥ k.
The given num does not contain any leading zero.
Example 1:

Input: num = "1432219", k = 3
Output: "1219"
Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.
Example 2:

Input: num = "10200", k = 1
Output: "200"
Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.
Example 3:

Input: num = "10", k = 2
Output: "0"
Explanation: Remove all the digits from the number and it is left with nothing which is 0.

k-digits.js

/**
 * @param {string} num
 * @param {number} k
 * @return {string}
 */
var removeKdigits = function(num, k) {
    let result = num;
    let c = 0
    let i = 0
    while (c < k) {
        if (i >= result.length-1) {
            result = result.substring(0, result.length-1)
            c++
        } else if (result[i] > result[i+1]) {
            result = result.substring(0, i) + result.substring(i+1)
            i = i - 1
            c++
        } else {
            i = i + 1
        }
    }
    
    return result.replace(/^0+/, "") || "0";
};

// Runtime: 56 ms
// Memory Usage: 41.6 MB
// 94.78%