Longest Palindromic Subsequence

LPS.js

/**
 * @param {string} s
 * @return {int}
 */
var longestPalindromeLength = function(s) { 'use strict'
  let n = s.length;
  if (n <= 1) return n;
  
  let L = {
    arr: [],
    get(i, j) {
      if (j < i) return 0;
      else if (j === i) return 1;
      else return this.arr[j][i];
    },
    set(i, j, val) {
      this.arr[j] = this.arr[j] || [];
      this.arr[j][i] = val;
    }
  };
  
  for (let d = 1; d < n; d++) {
    for (let i = 0; i < n-d; i++) {
      let j = i + d;
      let result;
      if (s[i] === s[j]) result = L.get(i+1, j-1) + 2;
      else result = Math.max(L.get(i+1, j), L.get(i, j-1));
      L.set(i, j, result);
    }
  }
  
  return L.get(0, n-1);
};