function levenshteinDistance( s1, s2 ) {
	var temp;
	var row;
	var pre;
	var m;
	var n;
	var i;
	var j;
	var k;

	if ( !isString( s1 ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', s1 ) );
	}
	if ( !isString( s2 ) ) {
		throw new TypeError( format( 'invalid argument. Second argument must be a string. Value: `%s`.', s2 ) );
	}
	n = s1.length;
	m = s2.length;

	// If either string is empty, the edit distance is equal to the number of characters in the non-empty string...
	if ( n === 0 ) {
		return m;
	}
	if ( m === 0 ) {
		return n;
	}

	row = [];
	for ( i = 0; i <= m; i++ ) {
		row.push( i );
	}

	for ( i = 0; i < n; i++ ) {
		pre = row[ 0 ];
		row[ 0 ] = i + 1;
		for ( j = 0; j < m; j++ ) {
			k = j + 1;
			temp = row[ k ];
			if ( s1[ i ] === s2[ j ] ) {
				row[ k ] = pre;
			} else {
				row[ k ] = min( pre, min( row[ j ], row[ k ] ) ) + 1;
			}
			pre = temp;
		}
	}
	return row[ m ];
}
Calculates the Levenshtein (edit) distance between two strings.

@param {string} s1 - first string value
@param {string} s2 - second string value
@throws {TypeError} first argument must be a string
@throws {TypeError} second argument must be a string
@returns {NonNegativeInteger} Levenshtein distance

@example
var distance = levenshteinDistance( 'algorithm', 'altruistic' );
// returns 6