-______-'s blog

Help In Question B. BerSU Ball ( Codeforces Round #277.5 )
By -______-, history, 7 years ago, In English

I've successfully solved this problem using Greedy Approach but in the editorial it was given that the probelm can also be solved using Dynamic Programming.

Can someone help me with the DP solution ? (preferably in C++)

Problem Link : http://codeforces.net/problemset/problem/489/B

Editorial Link : http://codeforces.net/blog/entry/14741

My Solution ( Greedy ) : 39216236

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7 years ago, # |
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First, sort arrays a and b.

Let dp[i][j] be the answer if we have only a[0..i] and b[0..j].

dp[i][j] is maximum of:

  • 0
  • 1 if |a[i]-b[j]|<=1
  • dp[i-1][j-1]+1 if i-1>=0, j-1>=0 and |a[i]-b[j]|<=1
  • dp[i-1][j] if i-1>=0
  • dp[i][j-1] if j-1>=0

Answer will be dp[n-1][m-1].

My Solution: 39227258

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    5 years ago, # ^ |
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    Can we do an O(n) dp ?

    Can we solve the problem Online (without brute-forces) ?

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    5 years ago, # ^ |
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    Here is my shorter dp solution O(n * m) ~ vector dp(n + 1, vi(m + 1, 0)); for (int i = 1; i <= n; ++i) for (int j = 1; j <= m; ++j) dp[i][j] = max({dp[i-1][j], dp[i][j-1], dp[i-1][j-1] + (abs(boy[i-1] — girl[j-1]) <= 1)}); ~

    Can we dp in O(n) if we use frequency array ?

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