北航C语言上机5

400+资料第五波
//1
/*
#include<stdio.h>
#include<stdlib.h>
int binary(int x,int b[],int len){
	int left=0,right=len;
	while(left<=right){
		int mid=(left+right)/2;
		if(x==b[mid]){
			return 0;
		}
		else if(x<b[mid])right=mid-1;
		else left=mid+1;
	}
	return 1;
}
int cmp(const void *a,const void *b){
	return *(int *)a-*(int *)b;
}
int main(){
    int a[100],b[100],x,i,j,k,p;
	k=0;
	while(~scanf("%d",&x)&&x!=-1){
        a[k++]=x;
	}
	p=k;
	k=0;
	while(~scanf("%d",&x)&&x!=-1){
		b[k++]=x;
	}
	qsort(b,k,sizeof(b[0]),cmp);
	for(i=0;i<p;i++){
		if(binary(a[i],b,k)){
            printf("%d ",a[i]);
		}
	}
	printf("\n");
	return 0;
}
*/
//2
/*
#include<stdio.h>
void itob(int n,char *s,int b){
    int i=0,j=0,t=0,fuhao=1;
	if(n<0){
		n=-n;
		fuhao=0;
	}
	while(n){
		s[i]=n%b+'0';
        if(s[i]>'9')s[i]+='a'-'9'-1;
		i++,n/=b;
	}
	if(fuhao==0){//负数
		s[i++]='-';
	}
	s[i--]='\0';
    for(;i>j;i--,j++){
		t=s[i];
		s[i]=s[j];
		s[j]=t;
	}
}
int main(){
    int n,b;
	char s[1000];
	scanf("%d%d",&n,&b);
	itob(n,s,b);
	printf("%s\n",s);
	return 0; 
}
*/
//3
/*
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
double getlen(double x1,double y1,double x2,double y2){
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
double getarea(int n,double x[],double y[]){
	double area=0,a,b,c,t;
	for(int i=2;i<n;i++){
        a=getlen(x[0],y[0],x[i],y[i]);
		b=getlen(x[0],y[0],x[i-1],y[i-1]);
		c=getlen(x[i],y[i],x[i-1],y[i-1]);
        t=(a+b+c)/2;
		area+=sqrt(t*(t-a)*(t-b)*(t-c));
	}
	return area;
}
int main(){
    int n,i;
	double x[50],y[50];
	scanf("%d",&n);
	for(i=0;i<n;i++)scanf("%lf%lf",&x[i],&y[i]);
	printf("%.2lf\n",getarea(n,x,y));
	return 0;
}
*/
//4
/*
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
int main(){
	char str[300],tmp;
	int i,j,n;
	scanf("%s%d",str,&n);
	int len=strlen(str);
    for(i=0;i<n;i++){
		for(j=0;j<len;j++){
			if(str[j]>=str[j-1]&&str[j]>str[j+1]){
                tmp=str[j];
				while(true){
					if(str[j+1]!='\0'){
                        tmp=str[j];str[j]=str[j+1];str[j+1]=tmp;j++;
					}
					if(str[j+1]=='\0'){
                        tmp=str[j];str[j]=str[j+1];str[j+1]=tmp;break;
					}
				}
				break;
			}
		}
       len--;
	}
	//str[len]='\0';
	printf("%s\n",str);
	return 0;
}
*/
//5
//6
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
int sp=0,st[1000];
void push(int t){
	if(sp<1000)
	st[sp++]=t;
}
int pop(){
	if(sp>0)
	return st[--sp];
	else return 0;
}
int main(){
	int n,i,j,tmp;
	int a[1000],t[1000];
    scanf("%d",&n);
	for(i=0;i<n;i++)scanf("%d",&a[i]);
	tmp=n,j=0;
	for(i=n-1;i>=0;i--){
        push(a[i]);
		while(sp>0&&st[sp-1]==tmp){
            t[j++]=pop();
			tmp--;
		}
	}
    bool ok=1;
	for(i=n-1,j=0;i>=0;i--,j++)
		if(t[i]!=j+1){ok=0;break;}
	if(ok)printf("YES\n");
	else printf("NO\n");
	return 0;
}