Games

coinsSums.js

/**
* Given an array of coins type, and an array of quatity for each type, 
* find out the possible sums.
*/
function Set() {
  this.set = {};
}
Set.prototype.add = function(value) {
  if (!this.set[value]) this.set[value] = true;
}
Set.prototype.toArray = function() {
  return Object.keys(this.set)
    .map(x => +x);
}

function generateSum(coins, quantity, i, sum, set) {
  set.add(sum);
  if (i === coins.length) return;
  if (quantity[i] === 0) generateSum(coins, quantity, i+1, sum, set);
  else {
    quantity[i]--;
    generateSum(coins, quantity, i, sum + quantity[i], set);
    quantity[i]++;
    generateSum(coins, quantity, i+1, sum, set);
  }
}

function main() {
  var coins = [10, 50, 100, 500];
  var quantity = [5, 3, 2, 2];
  var set = new Set();
  generateSum(coins, quantity, 0, 0, set);
  console.log(set.toArray().length);
}

main();

countPageDigits.js

/**
* Get the total digits count from 1 to n.
*/
function VanyaAndBook1s(n) {
    var c = 0;
    var leftLoops = ~~Math.log10(n) + 1;
    while (leftLoops > 0) {
        if (leftLoops === ~~Math.log10(n) + 1) {
            c += countLastPart(n);
        } else {
            c += countFirstPart(leftLoops);
        }
        leftLoops--;
    }
    return c;
}

function countFirstPart(leftLoops) {
    return (Math.pow(10, leftLoops) - Math.pow(10, leftLoops - 1)) * leftLoops
}

function countLastPart(n) {
    return (n - Math.pow(10, ~~Math.log10(n)) + 1) * (~~Math.log10(n) + 1);
}

/**
* shorter version
*/
VanyaAndBook1s = n => {
    s = m = (''+n).length
    while(m > 0)
        s += n - Math.pow(10, --m)
    return s
}

printSine.js

/**
* Print a full sine in m rows by n columns
*/
function printSine(m, n) {

	for (var i = -m; i < m; i++) {
		var char = '';
		for (var j = 0; j < 2 * Math.PI; j+= 2*Math.PI / n) {
			if (i === Math.floor(m*Math.sin(j + Math.PI))) char += '*';
			else char += ' ';
		} 
		console.log(char);
	}
}

printSine(10, 40)

validateSudoku.js

/**
* Find out if a 9x9 array[][] is a sudoku.
*/
function sudoku(grid) {

  var checkBlock = function(block) {
    var sample = '123456789';
    block.sort();
    if (block.join('') === sample) {
      return true;
    }
    return false;
  }

  var subgrids = [];

  for (var i = 0; i < 3; i++) {
    subgrids.push([]);
    for (var j = 0; j < 3; j++) {
      subgrids[i].push([]);
    }
  }

  for (var i = 0; i < 9; i++) {
    var horizontal = [];
    var vertical = [];
    for (var j = 0; j < 9; j++) {
      horizontal.push(grid[i][j]);
      vertical.push(grid[j][i]);
      subgrids[Math.floor(i / 3)][Math.floor(j / 3)].push(grid[i][j]);
    }
    if (!checkBlock(horizontal)) {
      return false;
    }
    if (!checkBlock(vertical)) {
      return false;
    }
  }

  for (var i = 0; i < 3; i++) {
    for (var j = 0; j < 3; j++) {
      if (!checkBlock(subgrids[i][j])) return false;
    }
  }

  return true;
}