TIOJ 1652, Alchemy. (98建中校內資訊能力競賽(prob3)) http://218.210.35.237:8080/JudgeOnline/showproblem?problem_id=1652

TIOJ1652.cpp

#include <cstdio>
#include <cstring>
#include <algorithm>

char l_exist[10000], r_exist[10000];
int n, m, val[10000], seq[10000];

int main() {
  int i, j, k, diff, ans = 0;
	scanf("%d", &n);
	for (i=0; i<n; i++) {
		scanf("%d", seq+i);
		val[i] = seq[i];
	}
	std::sort(val, val+n);
	for (i=m=1; i<n; i++)
		if (val[i-1] != val[i])
			val[m++] = val[i];
	for (i=0; i<n; i++) {
		seq[i] = std::lower_bound(val, val+m, seq[i]) - val;
	}
	for (i=0; i<n; i++) {
		memset(l_exist, 0, sizeof(l_exist));
		memset(r_exist, 0, sizeof(r_exist));
		diff = 0;
		for (j=i,k=i+1; j>=0 && k<n; j--,k++) {
			if (!l_exist[seq[j]]) {
				if (r_exist[seq[j]]) diff--;
				else diff++;
				l_exist[seq[j]] = 1;
			}
			if (!r_exist[seq[k]]) {
				if (l_exist[seq[k]]) diff--;
				else diff++;
				r_exist[seq[k]] = 1;
			}
			if (diff==0 && k-j+1>ans) ans =  k-j+1;
		}
	}
	printf("%d\n", ans);
	return 0;
}