How can I use CpModel to make three 1s appear in a 1D array ? (or-tools)

Question

I want three 1s to appear in the shift array，I wrote the following code：

model = cp_model.CpModel()
solver = cp_model.CpSolver()
shifts = {}
for i in range(5):
   shifts[(i)] = model.NewIntVar(0, 3, "shifts(%i)" % i)

for i in range(5):
    model.Add(sum([shifts[(i)]==1 for i in range(5) ]) == 3)

solver = cp_model.CpSolver()
status = solver.Solve(model)
for i in range(5):
    print(solver.Value(shifts[(i)]))

But it return: TypeError: unsupported operand type(s) for +: 'int' and 'BoundedLinearExpression'

Can anyboday help me ,please!

hi, Stradivari, my shifts's element must be integer like (0,1,2,3) ,My purpose is to make this array appear a certain number of integers。like three 1s or three 2s, how can I do it? — python.tong, Jul 04 '20 at 08:27

Stradivari · Answer 1 · 2020-07-04T13:58:37.303

Edit: As @Laurent Perron says, it is probably better to model your problem using booleans.

model = cp_model.CpModel()
solver = cp_model.CpSolver()
shifts = {}
values = range(3+1)

for i in range(5):
    for j in values:
        shifts[i, j] = model.NewBoolVar(f"{i} == {j}")
    # for each shift only 1 value is true
    model.Add(sum(shifts[i, j] for j in values) == 1)

# number of booleans where value is 1 == 3
model.Add(sum(shifts[i, 1] for i in range(5)) == 3)

solver = cp_model.CpSolver()
status = solver.Solve(model)
for i in range(5):
    for j in values:
        if solver.Value(shifts[i, j]):
            print(i, "==", j)

Original answer:

You can't sum constraints, create one boolvar per position, link the variables using model.Add(shifts[i]==1).OnlyEnforceIf(ones[i]) and constraint sum(ones) instead.

from ortools.sat.python import cp_model

model = cp_model.CpModel()
solver = cp_model.CpSolver()
shifts = {}
ones = {}
for i in range(5):
    shifts[i] = model.NewIntVar(0, 3, "shifts(%i)" % i)
    ones[i] = model.NewBoolVar("")
    model.Add(shifts[i] == 1).OnlyEnforceIf(ones[i])
    model.Add(shifts[i] != 1).OnlyEnforceIf(ones[i].Not())

model.Add(sum(ones.values()) == 3)

solver = cp_model.CpSolver()
status = solver.Solve(model)
for i in range(5):
    print(solver.Value(shifts[(i)]))

Most likely, remove the int vars, create 4 boolean vars with a sum == 1. — Laurent Perron, Jul 04 '20 at 12:42
Thank you very much Stradivari !!! I have another problem, I want the array to appear two 1s and three 2s simultaneously ，how can i do it? — python.tong, Jul 04 '20 at 12:44
as I said, remove the int var, replace each one by 4 boolvars, and sum these. — Laurent Perron, Jul 04 '20 at 13:49
I have another problem, I want the array to appear two 1s and three 2s simultaneously ，how can i do it? — python.tong, Jul 04 '20 at 14:44

How can I use CpModel to make three 1s appear in a 1D array ? (or-tools)

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