can we solve this problem https://mirror.codeforces.com/contest/96/problem/D using a single bfs with state (money, remaining distance)?

In order to get code jam's shirt, I have to be in top 1000. What algorithms do I need to learn to be in top 1000?. Do you guys have some problem that will likely come out in google code jam round 2?

https://mirror.codeforces.com/contest/447/problem/D .. My solution is greedy, everytime i get the biggest value from column or row and then add to the answer, I got wrong answer.. this is my submission https://mirror.codeforces.com/contest/447/submission/53039990

Can someone explain for me this problem? https://mirror.codeforces.com/contest/681/problem/D

If double can store larger value than long long, then why everyone rarely used double?

https://mirror.codeforces.com/gym/101911/problem/C . For each number in the array, I will merge each number from the array until it can't be merged, and then for each number in the array after it merged, I will multiply and then search for the number in the array, if it not found and the number is bigger than the maximum value on the array, then it will be no answer, I got wrong answer..

https://mirror.codeforces.com/problemset/problem/38/E . I solve with dp with 2 dimension where the first one is index and the second is 2 which is pin it or let it drop.. I compute current index result with previous result in this case index — 1 only, but I got wrong answer. Did anyone know why? here is my submission https://mirror.codeforces.com/contest/38/submission/50412221

https://training.ia-toki.org/problemsets/88/problems/459/