CS153/hw6/hw5programs/sp22_tests/ford_fulkerson.oat

struct Color {
  int white;
  int gray;
  int black
}

global cenum = new Color {white = 0; gray = 1; black = 2};   

global max = 9223372036854775807;

global n = 10; 

int min(int x, int y) {
    if (x < y) {
        return x;
    } else {
        return y;
    }
}

global head = 0;
global tail = 0;

void enqueue(int[] queue, int[] color, int x) {
  queue[tail] = x;
  tail = tail + 1;
  color[x] = cenum.gray;
  return;
}

int dequeue(int[] queue, int[] color) {
  var x = queue[head];
  head = head + 1;
  color[x] = cenum.black;
  return x;
}

bool bfs(int[][] capacity, int[][] flow, int[] pred, int start, int target) {
  var color = new int[n]{i -> cenum.white};
  var q = new int[n + 2]{i -> -1};

  head = 0;
  tail = 0;
  enqueue(q, color, start);
  pred[start] = -1;
  while (head != tail) {
    var u = dequeue(q, color);
    for (var v = 0; v < n; v = v + 1;) {
      if (color[v] == cenum.white & capacity[u][v] - flow[u][v] > 0) {
        enqueue(q, color, v);
        pred[v] = u;
      }
    }
  }
  return color[target] == cenum.black;
}

int fordFulkerson(int[][] capacity, int source, int sink) {
  var max_flow = 0;
  var flow = new int[][n]{i -> new int[n]{j -> 0}};
  var pred = new int[n]{i -> -1};

  while (bfs(capacity, flow, pred, source, sink)) {
    var increment = max;
    for (var u = n - 1; pred[u] >= 0; u = pred[u];) {
      increment = min(increment, capacity[pred[u]][u] - flow[pred[u]][u]);
    }
    for (var u = n - 1; pred[u] >= 0; u = pred[u];) {
      var t1 = flow[pred[u]][u];
      flow[pred[u]][u] = t1 + increment;
      var t2 = flow[u][pred[u]];
      flow[u][pred[u]] = t2 - increment;
    }
    max_flow = max_flow + increment;
  }
  return max_flow;
}

int program(int argc, string[] argv) {
 
    var capacity = new int[][n]{i -> new int[n]{j -> 0}};

    capacity[0][1] = 1;
    capacity[0][2] = 2;
    capacity[0][3] = 4;
    capacity[0][7] = 3;

    capacity[1][4] = 5;
    capacity[1][5] = 3;

    capacity[2][4] = 3;

    capacity[3][5] = 5;

    capacity[4][6] = 5;

    capacity[5][8] = 12;

    capacity[6][5] = 4;

    capacity[7][9] = 2;

    capacity[8][9] = 15;

    var s = 0;
    var t = 9;
    print_string("Max Flow: ");
    print_int(fordFulkerson(capacity, s, t));
    print_string(" flow.");
    return 0;  
}