1898-maximum-number-of-removable-characters.js

/**
 * @param {string} s
 * @param {string} p
 * @param {number[]} removable
 * @return {number}
 */
const maximumRemovals = function (s, p, removable) {
  const n = removable.length
  let l = 0,
    r = n
  while (l < r) {
    let mid = (l + r + 1) >> 1
    if (is_valid(s, p, removable, mid)) l = mid
    else r = mid - 1
  }
  return l
}

function is_valid(s, p, removable, cnt) {
  let len1 = s.length,
    len2 = p.length
  const check = Array(len1).fill(0)
  for (let i = 0; i < cnt; i++) check[removable[i]] = 1
  let ind1 = 0,
    ind2 = 0
  while (ind1 < len1 && ind2 < len2) {
    if (s[ind1] != p[ind2] || check[ind1]) {
      ind1++
      continue
    }
    ind1++, ind2++
  }
  return ind2 == len2
}

// another

/**
 * @param {string} s
 * @param {string} p
 * @param {number[]} removable
 * @return {number}
 */
const maximumRemovals = function(s, p, removable) {
  let l = 0, r = removable.length
  while(l < r) {
    const mid = r - Math.floor((r - l) / 2)
    if(valid(mid)) l = mid
    else r = mid - 1
  }
  return l
  
  function valid(mid) {
    let arr = s.split('')
    for (let i = 0; i < mid; i++) arr[removable[i]] = null
    arr = arr.filter(e => e !== null)
    
    for(let i = 0, j = 0; i < arr.length && j < p.length;) {
      if(arr[i] === p[j]) i++, j++
      else i++
      if(j === p.length) return true
    }
    return false
  }
};