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lecture 24
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11. LCS Example (0) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D X = ABCB; m = |X| = 4 Y = BDCAB; n = |Y| = 5 Allocate array c[5,4] ABCB BDCAB
12. LCS Example (1) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 for i = 1 to m c[i,0] = 0 for j = 1 to n c[0,j] = 0 ABCB BDCAB
13. LCS Example (2) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 0 A BCB B DCAB
14. LCS Example (3) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 0 0 0 A BCB B DC AB
15. LCS Example (4) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 0 0 0 1 A BCB BDC A B
16. LCS Example (5) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 0 0 0 1 1 A BCB BDCA B
17. LCS Example (6) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 0 0 1 0 1 1 A B CB B DCAB
18. LCS Example (7) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 1 1 1 A B CB B DCA B
19. LCS Example (8) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 1 1 1 2 A B CB BDCA B
20. LCS Example (10) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 2 1 1 1 1 1 1 AB C B BD CAB
21. LCS Example (11) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 2 1 1 1 1 1 2 AB C B BD C AB
22. LCS Example (12) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 AB C B BDC AB
23. LCS Example (13) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 1 ABC B B DCAB
24. LCS Example (14) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 1 1 2 2 ABC B B DCA B
25. LCS Example (15) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C B Yj B B A C D 0 0 0 0 0 0 0 0 0 0 if ( X i == Y j ) c[i,j] = c[i-1,j-1] + 1 else c[i,j] = max( c[i-1,j], c[i,j-1] ) 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 1 1 2 2 3 ABC B BDCA B
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29. Finding LCS j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C Yj B B A C D 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 1 1 2 2 3 B
30. Finding LCS (2) j 0 1 2 3 4 5 0 1 2 3 4 i Xi A B C Yj B B A C D 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1 2 1 1 1 1 2 1 2 2 1 1 2 2 3 B B C B LCS (reversed order): LCS (straight order): B C B (this string turned out to be a palindrome)
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32. Knapsack problem There are two versions of the problem: (1) “0-1 knapsack problem” and (2) “Fractional knapsack problem” (1) Items are indivisible; you either take an item or not. Solved with dynamic programming (2) Items are divisible: you can take any fraction of an item. Solved with a greedy algorithm .