Che cos’è un algoritmo in informatica?

Algoritmo: chi è appassionato di informatica non può non aver mai sentito questo termine. Anche i meno esperti ne avranno sentito parlare, soprattutto in ambito di programmazione. Ma che cos’è un algoritmo? Ora proveremo a spiegarvelo.

Un algoritmo è una procedura o una formula per risolvere un problema, basata sulla conduzione di una sequenza di azioni specifiche. Un programma per computer  può essere visto come un algoritmo elaborato. In matematica e informatica, un algoritmo di solito significa una piccola procedura che risolve un problema ricorrente.Essi sono ampiamente utilizzati in tutte le aree dell’informatica. Ad esempio, un algoritmo di un motore di ricerca utilizza come stringa di ricerca stringhe di parole chiave e  operatori, cerca il database associato per le pagine Web pertinenti e restituisce i risultati.Un algoritmo di crittografia trasforma i dati in base ad azioni specifiche per proteggerli. Ad esempio, un algoritmo a chiave segreta come DES (Data Encryption Standard ) del Dipartimento della Difesa statunitense utilizza la stessa chiave per crittografare e decrittografare i dati. Finché l’algoritmo è sufficientemente sofisticato, nessuno di quelli che non ha la chiave può decifrare i dati.

Le proprietà degli algoritmi

  • i passi devono essere elementari, cioè non possono essere ulteriormente divisibili (atomicità);
  • i passi non possono essere interpretati in altri modi (non ambiguità);
  • deve per forza essere svolto in un certo numero di specifici passi e, allo stesso tempo, deve richiedere in ingresso soltanto una determinata quantità di dati (finitezza);
  • l’esecuzione deve terminare entro un certo periodo di tempo (terminazione);
  • l’esecuzione deve portare ad un risultato univoco (effettività);
  • ogni passo deve essere ben stabilito (determinismo).

Diagrammi di flusso

A volte, per mostrare la procedura seguita da un certo algoritmo, potrebbe anche essere adoperato un cosiddetto diagramma di flusso. Un diagramma di flusso è una rappresentazione grafica delle operazioni da eseguire per l’esecuzione di un programma Per rappresentare i diversi concetti, nella maggior parte dei casi questi diagrammi di flusso utilizzano infatti cinque distinti blocchi:

  • inizio;
  • ingresso/uscita;
  • elaborazione;
  • controllo;
  • fine.

Ecco un esempio di diagramma di flusso per chiarirti le idee.

Risultati immagini per diagramma di flusso

 

Curiosità

La parola algoritmo deriva dal nome del matematico Mohammed ibn-Musa al-Khwarizmi, che faceva parte della corte reale di Baghdad e che visse tra il 780 e l’850 circa. Egli scrisse “Regole di ripristino e riduzione“, dove fece riferimento a questo concetto.

 

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