Prerequisite – Bubble Sort

**Problem –** Write an assembly language program in 8085 microprocessor to sort a given list of n numbers using Bubble Sort.

**Example –**

**Assumption –** Size of list is stored at 2040H and list of numbers from 2041H onwards.

**Algorithm –**

- Load size of list in C register and set D register to be 0
- Decrement C as for n elements n-1 comparisons occur
- Load the starting element of the list in Accumulator
- Compare Accumulator and next element
- If accumulator is less than next element jump to step 8
- Swap the two elements
- Set D register to 1
- Decrement C
- If C>0 take next element in Accumulator and go to point 4
- If D=0, this means in the iteration, no exchange takes place consequently we know that it won’t take place in further iterations so the loop in exited and program is stopped
- Jump to step 1 for further iterations

**Program –**

Address | Label | Instruction | Comment |
---|---|---|---|

2000H | START | LXI H, 2040H | Load size of array |

2003H | MVI D, 00H | Clear D register to set up a flag | |

2005H | MOV C, M | Set C register with number of elements in list | |

2006H | DCR C | Decrement C | |

2007H | INX H | Increment memory to access list | |

2008H | CHECK | MOV A, M | Retrieve list element in Accumulator |

2009H | INX H | Increment memory to access next element | |

200AH | CMP M | Compare Accumulator with next element | |

200BH | JC NEXTBYTE | If accumulator is less then jump to NEXTBYTE | |

200EH | MOV B, M | Swap the two elements | |

200FH | MOV M, A | ||

2010H | DCX H | ||

2011H | MOV M, B | ||

2012H | INX H | ||

2013H | MVI D, 01H | If exchange occurs save 01 in D register | |

2015H | NEXTBYTE | DCR C | Decrement C for next iteration |

2016H | JNZ CHECK | Jump to CHECK if C>0 | |

2019H | MOV A, D | Transfer contents of D to Accumulator | |

201AH | CPI 01H | Compare accumulator contents with 01H | |

201CH | JZ START | Jump to START if D=01H | |

201FH | HLT | HALT |

**Explanation-**

- Retrive an element in accumulator.
- Compare it with next element, if it is greater then swap otherwise move to next index.
- If in one entire loop there has been no exchange, halt otherwise start the whole iteration again.
- The following approach has two loops, one nested inside other so-
Worst and Average Case Time Complexity: O(n*n). Worst case occurs when array is reverse sorted.

Best Case Time Complexity: O(n). Best case occurs when array is already sorted.

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