different-ways-to-add-parentheses.cc

// Different Ways to Add Parentheses
#define REP(i, n) FOR(i, 0, n)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define ROF(i, a, b) for (int i = (b); --i >= (a); )

class Solution {
public:
  vector<int> diffWaysToCompute(string input) {
    vector<int> nums;
    vector<char> ops;
    for (int j = 0, i = 0; i < input.size(); i = j) {
      int x = 0;
      for (; j < input.size() && isdigit(input[j]); j++)
        x = x*10+input[j]-'0';
      nums.push_back(x);
      if (j < input.size())
        ops.push_back(input[j++]);
    }
    int n = nums.size();
    vector<vector<vector<int>>> s(n, vector<vector<int>>(n));
    REP(i, n)
      s[i][i].push_back(nums[i]);
    ROF(i, 0, n)
      FOR(j, i+1, n)
        FOR(k, i, j)
          for (auto x: s[i][k])
            for (auto y: s[k+1][j])
              s[i][j].push_back(op(ops[k], x, y));
    return s[0][n-1];
  }
  int op(char c, int x, int y) {
    switch (c) {
    case '+': return x+y;
    case '-': return x-y;
    default: return x*y;
    }
  }
};