I couldn't prove the greedy algorithm which used in the A part of [this](http://olympiads.win.tue.nl/ioi/ioi96/contest/ioi96j.html) problem, so I looked it up on the internet and found ([this)[](http://blog.m-s-t.org/2012/12/27/usaco-4-2-job-processing-analysis/]). There is a proof there, but I think that it's incomplete. Specifically, it doesn't prove subproblem needs to be solved optimally for problem to be solved optimally. Thanks for help in advance.↵
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Also, I'm really bad at greedy algorithms. Is there any text on proof techniques for greedy algorithms, must-solve problems, or other important stuff on greedy algorithms you know?
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Also, I'm really bad at greedy algorithms. Is there any text on proof techniques for greedy algorithms, must-solve problems, or other important stuff on greedy algorithms you know?