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Depth-first search (DFS) is an algorithm for traversing or searching a tree, tree structure, or graph. One starts at the root (selecting some node as the root in the graph case) and explores as far as possible along each branch before backtracking. A graph can be represented by its adjacency matrix G, where G[i][j] == 1 if there is an edge betwe…
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| .data | |
| Graph: .word 0,1,1,0,0,1,1,0,0 | |
| .word 1,0,0,0,0,0,0,0,0 | |
| .word 1,0,0,0,0,0,0,0,0 | |
| .word 0,0,0,0,1,1,0,0,0 | |
| .word 0,0,0,1,0,1,1,0,0 | |
| .word 1,0,0,1,1,0,0,0,0 | |
| .word 1,0,0,0,1,0,0,0,0 | |
| .word 0,0,0,0,0,0,0,0,0 | |
| .word 0,0,0,0,0,0,0,0,0 | |
| Graph2: .space 400 # temp array to store explored edges | |
| N: .word 0 # stores the array size | |
| Labels: .byte 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J' | |
| welcomemsg: .asciiz "Welcome to Depth First Search Traversal in MAL" | |
| inputmsg: .asciiz "\nEnter the root node: " | |
| linefeed: .asciiz "\n" | |
| .text | |
| .align 2 | |
| .globl main | |
| main: la $a0, welcomemsg # printf("%s", welcomemsg) | |
| li $v0, 4 | |
| syscall | |
| li $t0, 4 # Get the size of the graph | |
| la $s0, Graph # N = sqrt( (&graph2 - &graph)/4 ) | |
| la $s1, Graph2 | |
| sub $a0, $s1, $s0 | |
| div $a0, $a0, $t0 | |
| jal sqrt | |
| sw $v0, N | |
| input: li $v0, 4 | |
| la $a0, inputmsg | |
| syscall | |
| la $a0, Graph # &graph // Base address of the source graph | |
| lw $a1, N # size // Size of the Graph | |
| la $a2, Graph2 # &graph2 // Base address of the target graph | |
| jal InitGraph2 | |
| li $v0, 5 # take user input | |
| syscall | |
| move $a2, $v0 # root = input from user | |
| beq $a2, $zero, rdone # while ( root != 0 ) { | |
| lw $a1, N # size = Size of the Graph | |
| la $a0, Graph2 | |
| jal dfs # dfs(*graph2, size, root) | |
| j input # } | |
| dfs: addi $sp, $sp, -40 # adjust the stack | |
| sw $s5, 36($sp) # stores j ( temp pointer to graph ) | |
| sw $s4, 32($sp) # stores i ( counter variable ) | |
| sw $s3, 28($sp) # stores k = size * 4 | |
| sw $s2, 24($sp) # stores root | |
| sw $s1, 20($sp) # stores size | |
| sw $s0, 16($sp) # stores *graph | |
| sw $a2, 12($sp) # save a2 | |
| sw $a1, 8($sp) # save a1 | |
| sw $a0, 4($sp) # save a0 | |
| sw $ra, 0($sp) # save the return address ( to support recursion ) | |
| add $s0, $a0, $zero # saving the *graph | |
| add $s1, $a1, $zero # saving the size | |
| add $s2, $a2, $zero # saving the root | |
| li $s3, 4 # k = size * 4 | |
| mul $s3, $s3, $s1 | |
| add $a0, $zero, $s2 # printl(root) | |
| jal printl | |
| addi $s5, $s2, -1 # j = graph + ( (root - 1) * k ) | |
| mul $s5, $s5, $s3 | |
| add $s5, $s5, $s0 | |
| li $s4, 1 # i = 1 (counter) | |
| while1: bgt $s4, $s1, endloop1 # while ( i < size ) { | |
| sw $zero, ($s5) # *j = 0 | |
| addi $s5, $s5, 4 # j += 4 | |
| addi $s4, $s4, 1 # i++ | |
| j while1 # } | |
| endloop1: addi $s5, $s2, -1 # j = graph + ( ( root - 1 ) * 4 ) | |
| li $t1, 4 | |
| mul $s5, $s5, $t1 | |
| add $s5, $s5, $s0 | |
| li $s4, 1 # i = 1 (counter) | |
| while2: bgt $s4, $s1, endloop2 # while ( i < size ) { | |
| lw $t2, ($s5) # if ( *graph != 0 && i != root ) { | |
| beq $t2, $zero, L1 | |
| beq $s4, $s2, L1 | |
| move $a0, $s0 # dfs(*graph, size, i) | |
| move $a1, $s1 | |
| move $a2, $s4 | |
| jal dfs | |
| L1: addi $s4, $s4, 1 # } i++ | |
| add $s5, $s5, $s3 # j += k | |
| j while2 # } | |
| endloop2: lw $ra, 0($sp) | |
| lw $a0, 4($sp) | |
| lw $a1, 8($sp) | |
| lw $a2, 12($sp) | |
| lw $s0, 16($sp) | |
| lw $s1, 20($sp) | |
| lw $s2, 24($sp) | |
| lw $s3, 28($sp) | |
| lw $s4, 32($sp) | |
| lw $s5, 36($sp) | |
| addi $sp, $sp, 40 # pop items and adjust the stack pointer | |
| jr $ra | |
| InitGraph2: addi $sp, $sp, -16 # InitGraph2(*source, size, *target) | |
| sw $s0, 12($sp) # stores i // counter | |
| sw $a2, 8($sp) # save a2 // target | |
| sw $a1, 4($sp) # save a1 // size | |
| sw $a0, 0($sp) # save a0 // source | |
| mul $a1, $a1, $a1 # size = size * size | |
| li $s0, 1 # i = 1 // counter | |
| li $t1, 1 # j = 1 | |
| while3: bgt $s0, $a1, endloop3 # while ( i < size) { | |
| sw $zero, ($a2) # *target = 0 | |
| lw $t0, ($a0) | |
| bne $t0, $t1, L2 # if ( *target == j ) | |
| sw $t0, ($a2) # *source = j | |
| L2: addi $a0, $a0, 4 # source += 4 | |
| addi $a2, $a2, 4 # target += 4 | |
| addi $s0, $s0, 1 # i++ | |
| j while3 # } | |
| endloop3: lw $a0, 0($sp) | |
| lw $a1, 4($sp) | |
| lw $a2, 8($sp) | |
| lw $s0, 12($sp) | |
| addi $sp, $sp, 16 # pop items and adjust the stack pointer | |
| jr $ra | |
| printl: addi $sp, $sp, -8 # adjust stack to make room for 2 items | |
| sw $t0, 4($sp) # save register t0 to use afterwards | |
| sw $s0, 0($sp) # save register s0 to use afterwards | |
| la $s0, Labels | |
| addi $t0, $a0, -1 | |
| add $t0, $t0, $s0 | |
| lb $a0, ($t0) | |
| li $v0, 11 # Put | |
| syscall | |
| lw $s0, 0($sp) | |
| lw $t0, 4($sp) | |
| addi $sp, $sp, 8 | |
| jr $ra | |
| sqrt: addi $v0, $zero, 0 # r = 0 | |
| loop: mul $t0, $v0, $v0 # t0 = r*r | |
| bgt $t0, $a0, end # if (r*r > n) goto end | |
| addi $v0, $v0, 1 # r = r + 1 | |
| j loop # goto loop | |
| end: addi $v0, $v0, -1 # r = r - 1 | |
| jr $ra # return with r-1 in $v0 | |
| rdone: li $v0, 10 | |
| syscall |
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