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back to boardRecursion Posted by marat 19 Apr 2011 16:58 Let C[i][j] be weight of the edge( i, j). A( n, k ) - maximal amount of apples under k-th node after n cuts. B(k) - amount of edges under k-th node. Then ( k+ - right child and k- - left child of the k-th nod ) A(n,k) = max{ a(n - B(k-), k+ ), if ( n > B(k-)) } { a(n - B(k+), k- ), if ( n > B(k+)) } . { MAX i FROM( 0) TO (n) OF a(n-i,k+)+a(i,k-) + C[k][k-]+C[k][k+] } { A(0,k+) + A(0, k- ) + C[k][k-]+C[k][k+], if n = 0 } { - MAXAMOUNTOFAPPLES, if (k+ or k- doesn't exist AND n>0) } 1-th and 2-th lines: one can cut left or rigth edge, if so we have to cut n-B(k+-) edges in the other subtree. 3-th line: one can save both left and right edges, if so we have to cut i edges in left and n-i edges in the rigth subtrees. Choose maximal value changing i variable. 4-th line: in this case we should count amout of apples under k-th node. It's equal to amount of apples in subtrees plus edge weights. 5-th line: k is a leaf. if n>0 there is nothing to cut => deny this situation by MAXAMOUNTOFAPPLES with negative sign. I used MAXAMOUNTOFAPPLES = 3000000 After that - DP. Re: Recursion Can you write it on russian? |
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