UVA 10125 - Sumsets

链结：戳我。

AC了。这道题我参考了这里：狠狠地戳我。我觉得他的解释非常的棒:

　　找到a + b的和的所有情况。

　　然后看d - c在不在里面。

最后算法是O(n^2log(n))

View Code 
  1 /*
  2   Author: frankdj
  3   State: AC
  4 */
  5 #include <iostream>
  6 #include <cstring>
  7 #include <algorithm>
  8 using namespace std;
  9 
 10 struct Node{
 11     long long value;
 12     int x;
 13     int y;
 14 };
 15 
 16 const int kMaxNumEle = 1001;
 17 const int kMaxHashSize = 100000;
 18 
 19 Node sum[kMaxNumEle*kMaxNumEle];
 20 int elements[kMaxNumEle], num_element, num_sum;
 21 int head[kMaxHashSize], next[kMaxNumEle*kMaxNumEle];
 22 
 23 void InitLookupTable() {
 24     memset(head, 0, sizeof(head));
 25     memset(next, 0, sizeof(next));
 26 }
 27 
 28 int Hash(long long key) {
 29     return (int)((key & 0x7fffffff) % kMaxHashSize);
 30 }
 31 
 32 void Insert(int index) {
 33     int hash = Hash(sum[index].value);
 34     next[index] = head[hash];
 35     head[hash] = index;
 36 }
 37 
 38 bool IsDifferent(int i, int j, int index) {
 39     int x = sum[index].x;
 40     int y = sum[index].y;
 41     if (i == x || i == y || j == x || j == y)
 42         return false;
 43     else
 44         return true;
 45 }
 46 
 47 bool Find(long long number, int i, int j) {
 48     int hash = Hash(number);
 49     int index = head[hash];
 50     while (index != 0) {
 51         if (sum[index].value == number)
 52             if (IsDifferent(i, j, index))
 53                 return i;
 54             else
 55                 index = next[index];
 56         else
 57             index = next[index];
 58     }
 59     return false;
 60 }
 61 
 62 int Search() {
 63     for (int i = num_element; i >= 1; i--){
 64         for (int j = 1; j != i && j <= num_element; j++){
 65             if (Find(elements[i] - elements[j], i, j))
 66                 return i;
 67         }
 68     }
 69     return 0;
 70 }
 71 
 72 
 73 int main(int argc, char *argv[]){
 74 #ifndef ONLINE_JUDGE
 75     freopen("input.txt", "r", stdin);
 76 #endif
 77 
 78     while (cin >> num_element && num_element != 0) {
 79         memset(sum, 0, sizeof(sum));
 80         memset(elements, 0, sizeof(elements));
 81 
 82         for (int i = 1; i <= num_element; i++)
 83             cin >> elements[i];
 84 
 85         sort(elements+1, elements+num_element+1);
 86 
 87         num_sum = 1;
 88         for (int i = 1; i <= num_element; i++){
 89             for (int j = i+1; j <= num_element; j++){
 90                 sum[num_sum].value = elements[i] + elements[j];
 91                 sum[num_sum].x = i;
 92                 sum[num_sum].y = j;
 93                 Insert(num_sum);
 94                 num_sum++;
 95             }
 96         }
 97         num_sum--;
 98 
 99         int ans = Search();
100         if (ans != 0) {
101             cout << elements[ans] << endl;
102         }
103         else {
104             cout << "no solution" << endl;
105         }
106     }
107     return 0;
108 }

 

posted @ 2013-02-19 00:03  frankdj  阅读(304)  评论(0)  编辑  收藏  举报