留只脚印（DP）

题目链接：http://codeforces.com/problemset/problem/698/A

很久很久没做咯~~~~

　　dp 是个很神奇的东西。。。。

　　

 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 using namespace std;

 const int max_day =  + ;
 const int max_option = ;

 int dp[max_day][max_option];
 // 0:rest  1:contest/rest
 // 2:sport/rest  3:sport/contest/rest

 int main()
 {
     int n, a;
     #ifndef ONLINE_JUDGE
         freopen("in.txt", "r", stdin);
     #endif // ONLINE_JUDGE
     while (scanf("%d", &n) != EOF) {
         memset(dp, , sizeof(dp));

         for (int i = ; i <= n; i++) {
             scanf("%d", &a);

             // 呢个野要时时刻刻更新，选择最优来更新，甘样就保证到 dp[i][1]和dp[i][2]都系最好噶啦
             dp[i][] = max(dp[i-][], max(dp[i-][], dp[i-][]));
             if (a ==  || a == ) {
                 dp[i][] = max(dp[i-][], dp[i-][]) + ;   // +1 写出边，重要的事情说3遍！！！
             }

             if (a ==  || a == ) {
                 dp[i][] = max(dp[i-][], dp[i-][]) + ;
             }
      //       printf("dp[%d][0]=%d, dp[%d][1]=%d, dp[%d][2]=%d\n", i, dp[i][0], i,dp[i][1], i,dp[i][2]);
         }

         printf("%d\n", n-max(dp[n][], max(dp[n][], dp[n][])));

         /*  写错晒了。。。。脑退化 = =，好彩总算知道，dp[i][3] 系无鬼用的，后来知道左，改翻岩呢个细节，靠~ = =
         for (int i = 1; i <= n; i++) {
   //          dp[i][3] = max(dp[i-1][2], dp[i-1][1]) + 1;
             if (a[i] == 1) {   // contest
                 dp[i][0] = dp[i][1] = dp[i-1][2]+1;
                 dp[i][2] = dp[i-1][2];
             }
             else if (a[i] == 2) {  // sport
                 dp[i][0] = dp[i][2] = dp[i-1][1]+1;
                 dp[i][1] = dp[i-1][1];
      //           printf("dp[%d][2] = %d\n", i, dp[i][2]);
             }
             else if (a[i] == 0) {    // rest
                 dp[i][0] = dp[i-1][0];
                 dp[i][1] = dp[i-1][1];
                 dp[i][2] = dp[i-1][2];
        //         printf("dp[%d][0] = %d\n", i, dp[i][0]);
             }
             else {   // a[i] = 3  // s/r/c
                 if (a[i-1] == 2) {
                     dp[i][1] = dp[i-1][1] + 1;
                     dp[i][2] = dp[i-1][2];
                     dp[i][0] = dp[i-1][0];
                 }
                 else if (a[i-1] == 1) {
                     dp[i][2] = dp[i-1][2] + 1;
                 dp[i][0] = dp[i-1][0];
                 dp[i][1] = dp[i-1][1];
                 }

                 /*
                 if (a[i-1] == 0) {
                     dp[i][3] = dp[i-1][0];
                 }
                 else if (a[i-1] == 1) {
                     dp[i][3] = dp[i-1][2]+1;
                 }
                 else if (a[i-1] == 2) {
                     dp[i][3] = dp[i-1][1]+1;
                 }
                 else {
                     dp[i][3] = max(dp[i-1][2], dp[i-1][1]) + 1;
                 }

   //

             }
                printf("dp[%d][0] = %d\n", i, dp[i][0]);
             printf("dp[%d][1] = %d\n", i, dp[i][1]);
             printf("dp[%d][2] = %d\n", i, dp[i][2]);
         }
         printf("\ndp[%d][0]=%d, dp[%d][1]=%d, dp[%d][2]=%d\n", n, dp[n][0], n,dp[n][1], n,dp[n][2]);
         */
     }
     return ;

 }