Create XOR_subsequencesc.cpp

Greedy/XOR_subsequencesc.cpp

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+#include <cstdio>
+#include <algorithm>
+#include <vector>
+#include <cstdlib>
+#include <ctime>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+const int MAXN = 100005, MAX = (1 << 16);
+
+int mem[MAXN], N, sum[MAXN];
+long long total[1 << 16];
+
+inline void walk(int digits) {
+	int n = (1 << digits);
+	for(int i = 1 ; i <= digits ; i++) {
+		int m = (1 << i);
+		int mh = m >> 1;
+		for(int r = 0 ; r < n ; r += m) {
+			int t1 = r;
+			int t2 = r + mh;
+			for(int j = 0 ; j < mh ; j++, t1++, t2++) {
+				long long u = total[t1];
+				long long v = total[t2];
+				total[t1] = u + v;
+				total[t2] = u - v;
+			}
+		}
+	}
+}
+
+int main() {
+	scanf("%d", &N);
+	for(int i = 1 ; i <= N ; i++) {
+		scanf("%d", &mem[i]);
+		sum[i] = sum[i - 1] ^ mem[i];
+	}
+
+	for(int i = 0 ; i <= N ; i++) {
+		total[sum[i]]++;
+	}
+
+	walk(16);
+	for(int i = 0 ; i < MAX ; i++) {
+		total[i] = total[i] * total[i];
+	}
+	walk(16);
+	for(int i = 0 ; i < MAX ; i++) {
+		total[i] /= MAX;
+	}
+	total[0] -= (N + 1);
+	for(int i = 0 ; i < MAX ; i++) {
+		total[i] /= 2.0;
+	}
+
+	int ans = 0;
+	long long best = 0;
+	for(int i = 0 ; i < MAX ; i++) {
+		if (total[i] > best) {
+			best = total[i];
+			ans = i;
+		}
+	}
+	printf("%d %lld\n", ans, best);
+	return 0;
+}