Since 1945, when the first nuclear bomb was exploded by the Manhattan PRoject team in the US, the number of nuclear weapons have soared across the globe. Nowadays,the crazy boy in FZU named AekdyCoin possesses some nuclear weapons and wanna destroy our world. Fortunately, our mysterious spy-net has gotten his plan. Now, we need to stop it. But the arduous task is obviously not easy. First of all, we know that the Operating system of the nuclear weapon consists of some connected electric stations, which forms a huge and complex electric network. Every electric station has its power value. To start the nuclear weapon, it must cost half of the electric network’s power. So first of all, we need to make more than half of the power diasbled. Our tanks are ready for our action in the base(ID is 0), and we must drive them on the road. As for a electric station, we control them if and only if our tanks stop there. 1 unit distance costs 1 unit oil. And we have enough tanks to use. Now our commander wants to know the minimal oil cost in this action. Input The first line of the input contains a single integer T, specifying the number of testcase in the file. For each case, first line is the integer n(1<= n<= 100), m(1<= m<= 10000), specifying the number of the stations(the IDs are 1,2,3…n), and the number of the roads between the station(bi-direction). Then m lines follow, each line is interger st(0<= st<= n), ed(0<= ed<= n), dis(0<= dis<= 100), specifying the start point, end point, and the distance between. Then n lines follow, each line is a interger pow(1<= pow<= 100), specifying the electric station’s power by ID order. Output The minimal oil cost in this action. If not exist print “impossible”(without quotes). Sample Input 2 2 3 0 2 9 2 1 3 1 0 2 1 3 2 1 2 1 3 1 3 Sample Output 5 impossible

題目大意：給定N個電站和M條雙向道路，現(xiàn)在坦克在0號電站，要去炸毀這些電站，問在路徑最短的情況下能不能炸毀超過所有電站發(fā)電量一半的電量？

思路：因為電站數(shù)量較少，先考慮用弗洛伊德算法求出最短路徑，然后把路徑看著每個電站的體積，發(fā)電量看做電站的價值，就變成了01背包問題，最后只要判斷能否炸毀超過一半電量就可以。

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