guess-number-higher-or-lower-ii.cc

// Guess Number Higher or Lower II
// optimization of 2D dynamic programming: http://artofproblemsolving.com/community/c296841h1273742
class Solution {
public:
  int getMoneyAmount(int n) {
    vector<vector<int>> a(n+1, vector<int>(n+1, 0));
    for (int j = 2; j <= n; j++) {
      deque<pair<int, int>> q;
      for (int k = j-1, i = j; --i; ) {
        while (a[i][k-1] > a[k+1][j]) k--;
        while (q.size() && k < q.front().second) q.pop_front();
        long t = a[i+1][j]+i;
        while (q.size() && q.back().first >= t) q.pop_back();
        q.emplace_back(t, i);
        a[i][j] = min(q.front().first, a[i][k]+k+1);
      }
    }
    return a[1][n];
  }
};