Codeforces Round #FF (Div. 2)-C. DZY Loves Sequences
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题目:http://codeforces.com/contest/447/problem/C
题意:要求求出序列中上升子序列的最大长度,可以更改或不更改一个数字。
思路:关键求出两数组,up【】以当前数字为开头向右的上升序列长度,dw【】以当前数字结尾的向左的上升序列长度。---新技能!!
CODE:
#include <iostream>#include<stdio.h>#include<cmath>const int inf=0xffffff;using namespace std;int a[100005];int up[100005],dw[100005];int main(){ //freopen("in.in","r",stdin); int N; while(~scanf("%d",&N)) { for(int i=0;i<N;i++) scanf("%d",&a[i]); if(N==1) {printf("1\n");continue;} up[N-1]=1; dw[0]=1; for(int i=1;i<N;i++) { if(a[i-1]<a[i]) dw[i]=dw[i-1]+1; else dw[i]=1; } for(int i=N-2;i>=0;i--) { if(a[i+1]>a[i]) up[i]=up[i+1]+1; else up[i]=1; } int maxn=max(up[1],dw[N-2])+1; for(int i=1;i<N-1;i++) { if(a[i-1]+1<a[i+1])//此条件的判断很重要,说明此位置更改后可以将前后连接起来 maxn=max(maxn,up[i+1]+dw[i-1]+1); else maxn=max(maxn,max(dw[i-1]+1,up[i+1]+1)); } printf("%d\n",maxn); } return 0;}
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