題目鏈接：http://poj.org/problem?id=1678

動態博弈。用dp[i]來表示如果先行者首先選擇第i個數字的話能取得的最大差值。由於每次選擇的數字一定比上一次選擇的數字大，所以先對數組進行排序。然後對於每個數字，如果先行者首先選擇這個數字的話，dp[i] 初始化的值為num[i].然後在num[i]之後的序列中，如果有符合條件的數字的話，那麽選擇dp值最大的那個數字。最後對所有的數字進行for loop，尋找符合條件的並且差值最大的數字。代碼如下：

 1 //============================================================================
 
 2 // Name        : test.cpp
 3 // Author      : 
 4 // Version     :
 5 // Copyright   : Your copyright notice
 6 // Description : Hello World in C++, Ansi-style
 7 //============================================================================
 8 
 9 #include <iostream>
10 #include <math.h>
11 #include <stdio.h>
12
 
 #include <cstdio>
13 #include <algorithm>
14 #include <string.h>
15 #include <string>
16 #include <sstream>
17 #include <cstring>
18 #include <queue>
19 #include <vector>
20 #include <functional>
21 #include <cmath>
22 #include <set>
23
 
 #define SCF(a) scanf("%d", &a)
24 #define IN(a) cin>>a
25 #define FOR(i, a, b) for(int i=a;i<b;i++)
26 #define Infinity 999999999
27 #define NInfinity -999999999
28 #define PI 3.14159265358979323846
29 typedef long long Int;
30 using namespace std;
31 
32 int main()
33 {
34     int t;
35     int n, a, b;
36     SCF(t);
37     int num[10005];
38     int dp[10005];
39     while (t--)
40     {
41         SCF(n);
42         SCF(a);
43         SCF(b);
44         FOR(i, 0, n)
45             SCF(num[i]);
46 
47         sort(num, num + n);
48 
49         for (int i = n - 1; i >= 0; i--)
50         {        
51             dp[i] = num[i];
52             bool first = true;
53             int maxNum = 0;
54             for (int j = i + 1; j < n; j++)
55             {
56                 int diff = num[j] - num[i];
57                 if (diff >= a && diff <= b)
58                 {
59                     if (first)
60                     {
61                         maxNum = dp[j];
62                         first = false;
63                     }
64                     else
65                         maxNum = max(maxNum, dp[j]);
66                 }
67             }
68             dp[i] = dp[i] - maxNum;
69         }
70         int maxAns = 0;
71         bool found = false;
72         for (int i = n - 1; i >= 0; i--)
73         {
74             if (num[i] >= a && num[i] <= b)
75             {
76                 if (!found)
77                 {
78                     maxAns = dp[i];
79                     found = true;
80                 }
81                 else
82                 {
83                     if (dp[i] > maxAns)
84                         maxAns = dp[i];
85                 }
86             }
87         }
88         printf("%d\n", maxAns);
89     }
90     return 0;
91 }

POJ 1678 I Love this Game