つらら

つらら.cpp

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

#define max(x,y) ((x>y)?x:y)
#define N_MAX 100000

using namespace std;

int len[N_MAX];
int data[N_MAX];

main(){
  int n,l;
  scanf("%d%d",&n,&l);

  for(int i=0;i<n;i++) scanf("%d",len+i);

  if(len[0] > len[1]) data[0] = l - len[0];
  if(len[n-2] < len[n-1]) data[n-1] = l - len[n-1];

  for(int i=1;i<n-1;i++){
    if(len[i] > len[i+1]){
      if(len[i-1] < len[i]){
	data[i] = l-len[i];
      }else {
	data[i] = data[i-1] + l - len[i];
      }
    }
  }

  for(int i=n-2;i>=1;i--){
    if(len[i] < len[i+1]){
      if(len[i-1] < len[i]){
	data[i] = data[i+1] + l - len[i];
      }else{
	data[i] = max(data[i], data[i+1] + l - len[i]);
      }
    }
  }

  if(len[0] < len[1]) data[0] = data[1] + l - len[0];
  if(len[n-2] > len[n-1]) data[n-1] = data[n-2] + l - len[n-1];

  sort(data,data+n);

  printf("%d\n", data[n-1]);
}