Poj 3185 the water bowls Gaussian deyuan

Gaussian elimination element + bitwise operation enumeration free variable element

#include <cstdio>#include <cstring>#include <algorithm>#include <map>#include <set>#include <bitset>#include <queue>#include <stack>#include <string>#include <iostream>#include <cmath>#include <climits>using namespace std;const int maxn = 30;int a[maxn][maxn], fid[maxn], fcnt;void Gauss() {for(int i = 0; i < 20; i++) {int k = i;while(a[k][i] == 0 && k < 20) k++;if(k >= 20) continue;for(int j = 0; j <= 20; j++) swap(a[i][j], a[k][j]);for(int j = 0; j < 20; j++) if(i != j && a[j][i] != 0) {for(int k = 0; k <= 20; k++) a[j][k] ^= a[i][k];}}}void pa() {for(int i = 0; i < 20; i++) {for(int j = 0; j <= 20; j++) {printf("%d ", a[i][j]);}puts("");}}int main() {while(1) {memset(a, 0, sizeof(a));for(int i = 0; i < 20; i++) {int ret = scanf("%d", &a[i][20]);if(ret == EOF) return 0;}for(int i = 0; i < 20; i++) {a[i][i] = a[i][max(i - 1, 0)] = a[i][min(i + 1, 19)] = 1;}Gauss();fcnt = 0;memset(fid, -1, sizeof(fid));for(int i = 0; i < 20; i++) {int nowsum = 0;for(int j = 0; j <= 20; j++) nowsum += a[i][j];if(nowsum == 0) fid[i] = fcnt++;}int ans = 1e9;for(int i = 0; i < (1 << fcnt); i++) {int nowans = 0;for(int j = 0; j < 20; j++) {int nows = 0;for(int k = 0; k < 20; k++) if(fid[k] != -1 && a[j][k]) {if((1 << fid[k]) & i) nows ^= 1;} if(nows != a[j][20]) nowans++;}int bcnt = 0;for(int j = 0; j < fcnt; j++) if(i & (1 << j)) bcnt++;ans = min(ans, nowans + bcnt);}printf("%d\n", ans);}return 0;}

　　

Poj 3185 the water bowls Gaussian deyuan