PAT T1017 The Best Peak Shape

动态规划找最长上升子序列，正反遍历一遍序列即可~

#include<bits/stdc++.h>
using namespace std;
const int maxn=10010;
int N;
int a[maxn];
int l[maxn];
int r[maxn];
int main () {
    scanf ("%d",&N);
    for (int i=0;i<N;i++) 
    scanf ("%d",&a[i]);
    int maxLength=0;
    int maxIndex;
    int maxValue;
    int mincha;
    for (int i=1;i<N;i++) {
        for (int j=i-1;j>=0;j--) 
        if (a[j]<a[i]) l[i]=max(l[i],l[j]+1);
    }
    for (int i=N-2;i>=0;i--) {
        for (int j=i+1;j<N;j++)
        if (a[j]<a[i]) r[i]=max(r[i],r[j]+1);
    }
    for (int i=1;i<N;i++) {
        if (l[i]==0||r[i]==0) continue;
        int len=l[i]+r[i]+1;
        if (len>maxLength) {
            maxLength=len;
            maxIndex=i;
            mincha=abs(l[i]-r[i]);
        } 
        else if (len==maxLength&&abs(l[i]-r[i])<mincha) {
            maxIndex=i;
            mincha=abs(l[i]-r[i]);
        }
    }
    if (maxLength==0) printf ("No peak shape");
    else printf ("%d %d %d",maxLength,maxIndex+1,a[maxIndex]);
    return 0;
}