UVa 11549 Open Credit System

题意：给出n个数，找出两个整数a[i],a[j](i < j),使得a[i] - a[j]尽量大

从小到大枚举j,在这个过程中维护a[i]的最大值

maxai晚于ans更新，

可以看这个例子

1 8 9 10 11

正确的应该是-1

如果更早更新的话，算出来就是0

用数组来存的

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include <cmath>
 #include<stack>
 #include<vector>
 #include<map>
 #include<set>
 #include<queue>
 #include<algorithm>
 using namespace std;

 typedef long long LL;
 const int INF = (<<)-;
 const int mod=;
 const int maxn=;

 int a[maxn];
 int n;

 int main(){
     int T;
     scanf("%d",&T);
     while(T--){
         scanf("%d",&n);
         for(int i = ;i < n;i++) scanf("%d",&a[i]);
         int ans = a[] - a[];
         int maxai = a[];
         for(int j = ;j < n;j++){
             ans = max(ans,maxai - a[j]);
             maxai = max(maxai,a[j]);
         //    printf("j = %d  maxai = %d  ans = %d\n",j,maxai,ans);
         }
         printf("%d\n",ans);
     }
     return ;
 }

边读边算的

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include <cmath>
 #include<stack>
 #include<vector>
 #include<map>
 #include<set>
 #include<queue>
 #include<algorithm>
 using namespace std;

 typedef long long LL;
 const int INF = (<<)-;
 const int mod=;
 const int maxn=;

 int main(){
     int T;
     scanf("%d",&T);
     while(T--){
         int n;
         scanf("%d",&n);

         int x,y,ans;
         scanf("%d %d",&x,&y);
         ans = x-y;
         int maxai = x;
         for(int i = ;i<n;i++){
             scanf("%d",&x);
             ans = max(ans,maxai - x);
             maxai = max(maxai,x);
         }
         printf("%d\n",ans);
     }
     return ;
 }