[10.23] CPS-S2019 simulation game summary

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I too hard

Game ideas

Portal

• T1: Because obviously you n n side, so n ² enumeration wave, then the answer is found to contribute to a continuous range segment and, like twice the difference.
• T2: Random Walk? ? ? Shoved a wave of random walk formula relies entirely on yy, correctness apparently did not, so I did not play. Then found that the direct Gaussian elimination 60 minutes.
• T3: meaning of the questions did not understand. . .

After the game digestion

• T1 open a small array of gg.
• T2 at constant optimization on the n- ³ water passed (without a dream I do not deserve to get more than 40 points). From the leaves up backwards like Gaussian elimination, because i disappear with the j, i have no son, leaving only the position of the father and grandfather has a value of i on the i-related, and j of the two positions there is also a certain value, so when the father does not eliminate some more position changes from 0 to something else. Time complexity and accuracy can be guaranteed.
• In fact there nlogn T2 practice.
• T3, is actually seeking a maximum of d, such that
  $\sum \frac {|i-d|*w_i} {S} =d,S=\sum w_i$
  Then suppose $f(d)=\sum {|i-d|*w_i}-d*S$ , to such $f(d)=0$
  found that this is a monotonically decreasing function because if d becomes large, the increment is smaller than the latter in front.
  Binary integer before looking for zero maintenance and use Fenwick tree can be found.
  And then a solution of the equation just fine.

to sum up

• Be sure to check the size of the array.
• Observe the nature of the subject, the desired title Gaussian elimination really is the most conventional way of routine.
• T3 except that Italy is a water problem. . . But I was wrong character tone for two days. . . Mentality collapse.