DP Codeforces Round #303 (Div. 2) C. Woodcutters

题目传送门

 /*
     题意：每棵树给出坐标和高度，可以往左右倒，也可以不倒
     问最多能砍到多少棵树
     DP：dp[i][0/1/2] 表示到了第i棵树时，它倒左或右或不动能倒多少棵树
     分情况讨论，若符合就取最大值更新，线性dp，自己做出来了:)
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>
 #include <iostream>
 using namespace std;

 typedef long long LL;

 const int MAXN = 1e5 + ;
 const int INF = 0x3f3f3f3f;
 LL x[MAXN], h[MAXN];
 LL dp[MAXN][];        //0-l 1-no 2-r

 int main(void)        //Codeforces Round #303 (Div. 2) C. Woodcutters
 {
     //freopen ("C.in", "r", stdin);

     int n;
     while (scanf ("%d", &n) == )
     {
         for (int i=; i<=n; ++i)
         {
             scanf ("%I64d%I64d", &x[i], &h[i]);
         }
         memset (dp, , sizeof (dp));
         dp[][] = dp[][] = ;
         if (x[] + h[] < x[])    dp[][] = ;
         for (int i=; i<=n; ++i)
         {
             LL tmp;
             tmp = max (dp[i-][], dp[i-][]);
             tmp = max (tmp, dp[i-][]);
             dp[i][] = tmp;
             if (x[i] - h[i] > x[i-])
             {
                 dp[i][] = max (dp[i-][], dp[i-][]) + ;
             }
             if (x[i] - x[i-] > h[i-] + h[i])
             {
                 dp[i][] = max (dp[i][], dp[i-][] + );
             }
             if (i < n && x[i] + h[i] < x[i+])
             {
                 dp[i][] = tmp + ;
             }
             if (i == n)    dp[i][] = tmp + ;
         }

         LL ans;
         ans = max (dp[n][], dp[n][]);
         ans = max (ans, dp[n][]);
         printf ("%I64d\n", ans);
     }

     return ;
 }