最简单的bsearch，然而我wa了无数次.......最晕的一次是输错数了-_- ps：两个小循环要全部遍历。因为有可能是14,0,-2,-16这样的情况。 1986516 2006-07-30 23:28:21 Accepted 1101 C++ 00:00.10 444K St.Crux   #include <stdio.h>#include <stdlib.h> int a[1000], n, wi, wj, wk, wu; int comp(const void *a, const void *b){    int aa = *(int*)a, bb = *(int*)b;    return aa > bb;} int main(){  //freopen("in.txt", "r", stdin); while(scanf("%d", &n) && n) {  int i, k, j, u;  for(i = 0; i < n; i ++)   scanf("%d", &a[i]);  qsort(a, n, sizeof(int), comp);  wi = 536870912;  if(n < 4)   goto out;  //o(n^3 * logn)  for(i = n - 1; i >= 0; i --)  {   for(k = n - 1; k >= 0; k --)   {      if(i == k) continue;    for(j = k - 1; j > 0; j --)    {     if(j == i) continue;     u = a[i] - a[k] - a[j];     if(u != a[i] && u != a[k] && u != a[j])     {      //if not equivalent then begin binary search      int h = n - 1, l = 0, mid;      while(l <= h)      {       mid = (h + l) / 2;       if(u > a[mid]) l = mid + 1;       else if(u < a[mid]) h = mid - 1;       else if(u == a[mid])        {        wi = a[i], wk = a[k], wj = a[j], wu = u;        goto out;       }            }     }    }   }  }out: if(wi == 536870912)   printf("no solution\n");  else   //printf("%d %d %d %d\n", wi, wk, wj, wu);   printf("%d\n", wi); } return 0;}  

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