BZOJ 1609 Usaco Eating Together

看完题目第一眼的感觉就是求一个最长不上升子序列和最长不下降子序列
O(N^2)一定是跑不过去的所以要写个O(NlogN)的算法
结果成功写挫~
思维难度不大，注意二分容易写爆炸。

#include <cstdio>
#include <algorithm>
#include <cstring>using namespace std;int n;
int num[30005],b[30005];
int Max,MAX;void DOWN(){Max = 1;int j;b[Max] = num[Max];for(int i=2;i<=n;i++){if(num[i]<=b[Max]) j = ++Max;else{int l = 1;int r = Max+1;while(l<r){int m = (l+r)>>1;if(b[m]>=num[i]) l = m+1;else r = m;}j = l;}b[j] = num[i];}/*for(int i=1;i<=Max;i++){printf("b[%d]:%d\n",i,b[i]);}*/MAX=Max;
}void UP(){memset(b,0,sizeof(b));Max = 1;int j ;b[Max] = num[Max];for(int i=2;i<=n;i++){if(num[i]>=b[Max]) j=++Max;else{int l = 1;int r = Max+1;while(l<r){int m = (l+r)>>1;if(b[m]<=num[i]) l = m+1;else r = m;}j= l;}b[j] = num[i];}/*for(int i=1;i<=Max;i++){printf("b[%d]:%d\n",i,b[i]);}*/MAX = max(Max,MAX);
}int main(){scanf("%d",&n);for(int i=1;i<=n;i++) scanf("%d",&num[i]);DOWN();UP();printf("%d\n",n-MAX);return 0;
}

转载于:https://www.cnblogs.com/OIerLYF/p/7496131.html

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