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

 

题目传送门

 1 /*  2  题意：每棵树给出坐标和高度，可以往左右倒，也可以不倒  3  问最多能砍到多少棵树  4  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  5  分情况讨论，若符合就取最大值更新，线性dp，自己做出来了:)  6 */  7 #include <cstdio>  8 #include <algorithm>  9 #include <cstring> 10 #include <cmath> 11 #include <iostream> 12 using namespace std; 13 14 typedef long long LL; 15 16 const int MAXN = 1e5 + 10; 17 const int INF = 0x3f3f3f3f; 18 LL x[MAXN], h[MAXN]; 19 LL dp[MAXN][3]; //0-l 1-no 2-r 20 21 int main(void) //Codeforces Round #303 (Div. 2) C. Woodcutters 22 { 23 //freopen ("C.in", "r", stdin); 24 25 int n; 26 while (scanf ("%d", &n) == 1) 27  { 28 for (int i=1; i<=n; ++i) 29  { 30 scanf ("%I64d%I64d", &x[i], &h[i]); 31  } 32 memset (dp, 0, sizeof (dp)); 33 dp[1][0] = dp[1][1] = 1; 34 if (x[1] + h[1] < x[2]) dp[1][2] = 1; 35 for (int i=2; i<=n; ++i) 36  { 37  LL tmp; 38 tmp = max (dp[i-1][0], dp[i-1][1]); 39 tmp = max (tmp, dp[i-1][2]); 40 dp[i][1] = tmp; 41 if (x[i] - h[i] > x[i-1]) 42  { 43 dp[i][0] = max (dp[i-1][0], dp[i-1][1]) + 1; 44  } 45 if (x[i] - x[i-1] > h[i-1] + h[i]) 46  { 47 dp[i][0] = max (dp[i][0], dp[i-1][2] + 1); 48  } 49 if (i < n && x[i] + h[i] < x[i+1]) 50  { 51 dp[i][2] = tmp + 1; 52  } 53 if (i == n) dp[i][2] = tmp + 1; 54  } 55 56  LL ans; 57 ans = max (dp[n][0], dp[n][1]); 58 ans = max (ans, dp[n][2]); 59 printf ("%I64d\n", ans); 60  } 61 62 return 0; 63 }