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Challenging Puzzle #45 - One Possible Solution Approach…
NB:  There is only one final solution to this Sudoku puzzle…
A B C D E F G H I
1                  
2 AA BB CC Reference to 3x3 Blocks AA, BB & CC
3                  
4                  
5 DD EE FF Reference to 3x3 Blocks DD, EE & FF
6                  
7                  
8 GG HH II Reference to 3x3 Blocks GG, HH & II
9                  
A B C D E F G H I
1       8   7       Challenging Puzzle #45 - November 14, 2005
2     7   3   2     Original puzzle as published © joe-ks.com
3 9   2       7   4
4 1 4           9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8     4 3   5 6   8
9       9   6      
A B C D E F G H I
1     3 8   7       Step 1: #3 is in Columns A & B: #3 MUST go in Cell C1...
2     7   3   2    
3 9   2       7 3 4 Step 2: #3 is now in Rows 1 & 2: #3 MUST go in Cell H3...
4 1 4       3   9 7
5 3               6 Step 3: #3 is now in Columns H & I: #3 MUST go in Cell G9...
6 7 2           5 3
7   3 1       9 4   Step 4: #3 is in Rows 5 & 6: #3 MUST go in Cell F4
8     4 3   5 6   8
9       9   6 3    
A B C D E F G H I
1     3 8 2 7       Step 4: #2 is in Rows 2 & 3: #2 MUST go in Cell E1...
2     7   3   2    
3 9   2       7 3 4 Step 5: #4 is in Rows 7 & 8: #4 MUST go in Cell E9...
4 1 4       3   9 7
5 3               6 Step 6: Block HH needs #1: #1 MUST go in Cell E8
6 7 2           5 3      (#1 in Row 7 @ C7 excludes use of Cells D7, E7 & F7)
7   3 1       9 4  
8     4 3 1 5 6   8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7       Step 7: Look @ Cell F3: only #1 can go in F3...
2     7   3   2    
3 9   2     1 7 3 4
4 1 4       3   9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8     4 3 1 5 6   8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7       Step 8: Look @ Cell G4: only #8 can go in G4...
2     7   3   2    
3 9   2     1 7 3 4
4 1 4       3 8 9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8     4 3 1 5 6   8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7       Step 9: Look @ Cell A8: only #2 can go in A8...
2     7   3   2    
3 9   2     1 7 3 4
4 1 4       3 8 9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8 2   4 3 1 5 6   8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7       Step 10: Look @ Cell H8: only #7 can go in H8...
2     7   3   2    
3 9   2     1 7 3 4
4 1 4       3 8 9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8 2   4 3 1 5 6 7 8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7       Step 11: Complete Row 8: #9 MUST go in Cell B8...
2     7   3   2    
3 9   2     1 7 3 4
4 1 4       3 8 9 7
5 3               6
6 7 2           5 3
7   3 1       9 4  
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3    
A B C D E F G H I
1 456 156 3 8 2 7 15 16 159 Look at all possibilites for vacant cells…
2 4568 1568 7 456 3 49 2 168 159 Step 12: in Block BB, #9 is unique to Block: #9 MUST go in F2
3 9 568 2 56 56 1 7 3 4 Step 13: in Block CC, #8 is unique to Block: #8 MUST go in H2
4 1 4 56 256 56 3 8 9 7 Step 14: in Block DD, #6 is unique to Block: #6 MUST go in C4
5 3 58 589 12457 5789 2489 14 12 6 Step 15: in Block FF, #2 is unique to Block: #2 MUST go in H5
6 7 2 689 146 689 489 14 5 3
7 568 3 1 27 78 28 9 4 25
8 2 9 4 3 1 5 6 7 8
9 58 578 58 9 4 6 3 12 125
A B C D E F G H I
1     3 8 2 7      
2     7   3 9 2 8  
3 9   2     1 7 3 4
4 1 4 6     3 8 9 7
5 3             2 6
6 7 2           5 3
7   3 1       9 4  
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7     9 Step 16: #9 is in Rows 2 & 3: #9 MUST go in Cell I1
2     7   3 9 2 8        (#9 in Column G @ G7 excludes use of Cell G1, &
3 9   2     1 7 3 4      #9 in Column H @ H4 excludes use of Cell H1)
4 1 4 6     3 8 9 7
5 3             2 6 Step 17: #6 is in Rows 8 & 9: #6 MUST go in Cell A7...
6 7 2           5 3
7 6 3 1       9 4  
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3    
A B C D E F G H I
1     3 8 2 7   6 9 Step 18: Complete Column H: need #s 1 & 6…
2     7   3 9 2 8         #6 can't go in Cell H9 (cf #6 in Row 9 @ F9), so
3 9   2     1 7 3 4      #6 MUST go in Cell H1, & therefore #1 MUST go in Cell H9
4 1 4 6     3 8 9 7
5 3             2 6
6 7 2           5 3
7 6 3 1       9 4  
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1  
A B C D E F G H I
1     3 8 2 7   6 9 Step 19: Look @ Cell E4: only #5 can go in E4...
2     7   3 9 2 8  
3 9   2     1 7 3 4 Step 20: Complete Row 4: #2 MUST go in Cell D4...
4 1 4 6 2 5 3 8 9 7
5 3             2 6 Step 21: #2 is now in Columns D & E: #2 MUST go in Cell F7...
6 7 2           5 3
7 6 3 1     2 9 4   Step 22: #2 is now in Rows 7 & 8: #2 MUST go in Cell I9...
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1 2
A B C D E F G H I
1     3 8 2 7 5 6 9 Step 23: Complete Column I: need #s 1 & 5…
2     7   3 9 2 8 1      #1 can't go in Cell I7 (cf #1 in Row 7 @ C7), so
3 9   2     1 7 3 4      #1 MUST go in Cell I2, & therefore #5 MUST go in Cell I7
4 1 4 6 2 5 3 8 9 7
5 3             2 6 Step 24: #5 is now in Columns H & I: #5 MUST go in Cell G1...
6 7 2           5 3
7 6 3 1     2 9 4 5
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1 2
A B C D E F G H I
1     3 8 2 7 5 6 9 Step 25: Complete Row 7: need #s 7 & 8…
2     7   3 9 2 8 1      #8 can't go in Cell D7 (cf #8 in Column D @ D1), so
3 9   2     1 7 3 4      #8 MUST go in Cell E7, & therefore #7 MUST go in Cell D7
4 1 4 6 2 5 3 8 9 7
5 3             2 6
6 7 2           5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1 2
A B C D E F G H I
1   1 3 8 2 7 5 6 9 Step 26: #1 is in Columns A & C: #1 MUST go in Cell B1
2     7   3 9 2 8 1     (#1 in Row 2 @ I2 excludes use of Cell B2, &
3 9   2     1 7 3 4        #1 in Row 3 @ F3 excludes use of Cell B3)
4 1 4 6 2 5 3 8 9 7
5 3             2 6
6 7 2           5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 27: Look @ Cell E3: only #6 can go in Cell E3…
2     7   3 9 2 8 1
3 9   2   6 1 7 3 4 Step 28: #6 is now in Columns E & F: #6 MUST go in Cell D6
4 1 4 6 2 5 3 8 9 7      (cf #6 in Row 5 @ I5 excludes use of Cell D5)
5 3             2 6
6 7 2   6       5 3 Step 29: Complete Row 1: #4 MUST go in Cell A1
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9       9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 30: Complete Column A: need #s 5 & 8…
2 5   7   3 9 2 8 1      #8 can't go in Cell A2 (cf #8 in Row 2 @ H2), so
3 9   2   6 1 7 3 4      #8 MUST go in Cell A9, & therefore #5 MUST go in Cell A2
4 1 4 6 2 5 3 8 9 7
5 3             2 6
6 7 2   6       5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9 8     9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 31: Complete Row 9: need #s 5 & 7…
2 5   7   3 9 2 8 1      #7 can't go in Cell C9 (cf #7 in Column C @ C2), so
3 9   2   6 1 7 3 4      #7 MUST go in Cell B9, & therefore #5 MUST go in Cell C9
4 1 4 6 2 5 3 8 9 7
5 3       7     2 6 Step 32: Complete Column E: need #s 7 & 9…
6 7 2   6 9     5 3      #7 can't go in Cell E6 (cf #7 in Row 6 @ A6), so
7 6 3 1 7 8 2 9 4 5      #7 MUST go in Cell E5, & therefore #9 MUST go in Cell E6
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 33: Complete Column C: need #s 8 & 9…
2 5   7   3 9 2 8 1      #9 can't go in Cell C6 (cf #9 in Row 6 @ E6), so
3 9   2   6 1 7 3 4      #9 MUST go in Cell C5, & therefore #8 MUST go in Cell C6
4 1 4 6 2 5 3 8 9 7
5 3   9   7     2 6
6 7 2 8 6 9     5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 34: Complete Column F: need #s 4 & 8…
2 5   7   3 9 2 8 1      #8 can't go in Cell F6 (cf #8 in Row 6 @ C6), so
3 9   2   6 1 7 3 4      #8 MUST go in Cell F5, & therefore #4 MUST go in Cell F6
4 1 4 6 2 5 3 8 9 7
5 3   9   7 8 4 2 6 Step 35: Complete Row 6: #1 MUST go in Cell G6...
6 7 2 8 6 9 4 1 5 3
7 6 3 1 7 8 2 9 4 5 Step 36: Complete Column G: #4 MUST go in Cell G5...
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 37:  Complete Row 5: need #s 1 & 5…
2 5   7   3 9 2 8 1      #1 can't go in Cell B5 (cf #1 in Column B @ B1), so
3 9   2   6 1 7 3 4      #1 MUST go in Cell D5, & therefore #5 MUST go in Cell B5
4 1 4 6 2 5 3 8 9 7
5 3 5 9 1 7 8 4 2 6
6 7 2 8 6 9 4 1 5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 38: Complete Row 3: need #s 5 & 8…
2 5   7   3 9 2 8 1      #5 can't go in Cell B3 (cf #5 in Column B @ B5), so
3 9 8 2 5 6 1 7 3 4      #5 MUST go in Cell D3, & therefore #8 MUST go in Cell B3
4 1 4 6 2 5 3 8 9 7
5 3 5 9 1 7 8 4 2 6
6 7 2 8 6 9 4 1 5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 Step 39:  Complete Row 2 (& Puzzle): need #s 4 & 6…
2 5 6 7 4 3 9 2 8 1      #4 can't go in Cell B2 (cf #4 in Column B @ B4), so
3 9 8 2 5 6 1 7 3 4      #4 MUST go in Cell D2, & therefore #6 MUST go in Cell B2
4 1 4 6 2 5 3 8 9 7
5 3 5 9 1 7 8 4 2 6
6 7 2 8 6 9 4 1 5 3
7 6 3 1 7 8 2 9 4 5
8 2 9 4 3 1 5 6 7 8
9 8 7 5 9 4 6 3 1 2
A B C D E F G H I
1 4 1 3 8 2 7 5 6 9 45 Final Proof:
2 5 6 7 4 3 9 2 8 1 45      - All Rows add up to 45;
3 9 8 2 5 6 1 7 3 4 45
4 1 4 6 2 5 3 8 9 7 45
5 3 5 9 1 7 8 4 2 6 45
6 7 2 8 6 9 4 1 5 3 45
7 6 3 1 7 8 2 9 4 5 45
8 2 9 4 3 1 5 6 7 8 45
9 8 7 5 9 4 6 3 1 2 45
 
45 45 45 45 45 45 45 45 45        - All Columns add up to 45;
45 45 45      - All 3x3 Blocks add up to 45…
45 45 45
45 45 45

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