regexMatching

regexMatching.js

function isMatch(text, pattern) {
  var truthTable = [];
  var textArr = text.split('');
  var patternArr = pattern.split('');

  
  function initRowArray() {
    var newArr = [];
    for(var i = 0; i <= patternArr.length + 1; i++) {
      newArr[i] = null;
    }
    return newArr;
  }

  // Initialize truthTable
  for(var i = 0; i <= textArr.length + 1; i++) {
    truthTable.push(initRowArray());
  }

  // Set first pair to true where we handle
  // a* or a*b*
  truthTable[0][0] = true;

  for(var i = 1; i < truthTable.length; i++) {
    for(var j = 1; j < truthTable[0].length; j++) {
      if(patternArr[j-1] === '.' || patternArr[j-1] === textArr[i-1]) {
        truthTable[i][j] = truthTable[i-1][j-1];
      } else if(pattern[j-1] === '*') {
        truthTable[i][j] = truthTable[i][j-2];
        if(patternArr[j-2] === '.' || patternArr[j-2] === textArr[i-1]) {
          truthTable[i][j] = truthTable[i][j] || truthTable[i-1][j];
        }
      } else {
        truthTable[i][j] = false;
      }
    }
  }
  
  
  console.log('*****');
  console.log(truthTable);
  return truthTable[textArr.length][patternArr.length];
}

console.log("isMatch", isMatch('a', 'a*'));