Educational Codeforces Round 30 B. Balanced Substring
2017-10-15 16:02
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题目链接
http://codeforces.com/contest/873/problem/B题目大意
给你一串01字符串(n <= 1e5),让你找出最长的连续的一段子串,且子串中0和1的个数相同思路
这题和lis很像,所以一开始我一直往dp方向去想了,一直没做出来其实这题很简单,我们去统计0和1个数的前缀和,在for一遍的同时,把0和1前缀和的差值对应的位置记下来,如果后面又出现有相同差值的情况,那么中间一段就是符合题意的子串了(这是核心思想,请务必搞明白)
代码
#include<bits/stdc++.h> using namespace std; int cnt[200005]; char s[100005]; int main() { memset(cnt, -1, sizeof(cnt)); int n, t0 = 0, t1 = 0, ans = 0, cur = 100000; scanf("%d %s", &n, s+1); cnt[cur] = 0; for(int i=1; i<=n; ++i) { if(s[i] == '0') ++t0; else if(s[i] == '1') ++t1; if(cnt[t1-t0+cur] != -1) ans = max(ans, i - cnt[t1-t0+cur]); else cnt[t1-t0+cur] = i; } printf("%d\n", ans); return 0; }
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