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题意：输入unsigned int N,L,U,找出一个M(L<=M<=U)使得N | M最大,如果有多个M使得N | M最大,取最小的M,
解题思路:贪心，从最高位开始,判断是否应该置为0还是置为1,如果置0,那么一定要判断当前的ans加上剩下的数是否还在[L,U]之间.
如果不在,一定要置1.
#include "pch.h"#include #include #include #include #include #include #include #include #include #include #include #include namespace cc{ using std::cout; using std::endl; using std::cin; using std::map; using std::vector; using std::string; using std::sort; using std::priority_queue; using std::greater; using std::vector; using std::swap; using std::stack; using std::bitset; unsigned int N, L, U; unsigned int a[32]; void init() { for (int i=0;i<32;i++) { a[i] = (1 << i) - 1; } } int findMaxBit(unsigned U) { int max = 0; int i = 0; while (i < 32) { if ((U >> i) & 1) max = i; ++i; } return max; } void solve() { init(); while (cin>>N>>L>>U) { unsigned int ans = 0; unsigned int curMax = N; int mb = findMaxBit(U); while (mb+1) { unsigned int cur = 1 << mb; if ((cur & N) == cur) { //same 1 //check is need this bit to 1 if ((ans | a[mb]) < L && (ans|cur) <= U) { ans = ans | cur; } } else { //N的这位为0 if ((ans | cur) <= U) { ans = ans | cur; } } --mb; } cout << ans << endl; } }};int main(){#ifndef ONLINE_JUDGE freopen("d://1.text", "r", stdin);#endif // !ONLINE_JUDGE cc::solve(); return 0;}
转载于:https://www.cnblogs.com/shuiyonglewodezzzzz/p/10206650.html