Codeforces 437B The Child and Set
题目链接:Codeforces 437B The Child and Set
開始是想到了这样的情况,比方lowbit之后从大到小排序后有这么几个数,200。100,60。50。S = 210。那先选了200肯定就不行了,所以写了个DFS。果断TLE。后来想了想lowbit之后的值都是最高位是1。其余位都是0的二进制数,所以上边的情况是不会出现的,至于原因我感觉我说不清楚。。
#include <iostream> #include <cstdio> #include <vector> #include <cstring> #include <algorithm> using namespace std; const int MAX_N = 100000 + 100; struct Node { int val, i; }; Node arr[MAX_N]; int cmp(Node a, Node b) { return a.val > b.val; } int lowbit(int x) { return x & (-x); } int s, limit,sum = 0; int path[MAX_N], num; int main() { scanf("%d%d", &s, &limit); for(int i = limit; i >= 1; i--) { arr[i].val = lowbit(i); arr[i].i = i; } sort(arr + 1, arr + 1 + limit, cmp); int sum = 0; for(int i = 1; i <= limit; i++) { if(arr[i].val + sum > s) continue; sum += arr[i].val; path[num++] = arr[i].i; if(sum == s) break; } if(sum == s) { printf("%d\n", num); printf("%d", path[0]); for(int i = 1; i < num; i++) printf(" %d", path[i]); puts(""); } else puts("-1"); return 0; }