Matrix memoization

mmemoization.js

class Matrix {
  
  constructor() {
    this.matrix = [
      [false, false, false, false],
      [false, true,  false, false],
      [false, true,  false, false],
      [false, false, false, false]
    ];
  }
  
  isValidPath(row, col) {
    return this.matrix[row] === undefined || 
        this.matrix[row][col] === undefined ||
        this.matrix[row][col] === true;
  }
  
  isEnd(row, col) {
    return row === this.matrix.length - 1 && col === this.matrix[0].length - 1;
  }
  
  /**
   * Find the number of paths to the end of the matrix.
   * Normally: Time O(2^n^2)
   * With memoization: Time O(n^2)
   */
  countPaths(row, col, cache = []) {    
    if (this.isValidPath(row, col)) {
      return 0;
    }
    
    if (this.isEnd(row, col)) {
      return 1;
    }
    
    if (!cache[row] || !cache[row][col]) {
      if (!cache[row]) {
        cache[row] = [];
      }        
      cache[row][col] = this.countPaths(row + 1, col) + this.countPaths(row, col + 1);
    }
    
    return cache[row][col];
  }
}

const test = (currentResult, expectedResult) => {
  if (currentResult !== expectedResult) {
    console.log('Error!');
  } else {
    console.log('Success.');
  }
} 

var obj = new Matrix();

console.log(test(obj.countPaths(0, 0), 5));