uniform distribution of a set of characters

Question

There is a set of characters that needs to be uniformly distributed in an array. For example,

a - 1

b - 2

c - 3

d - 4

In this case there

Answer 1

You could use something similar to the bresenham algorithm to track the error between the ideal spacing and the last spacing for each component:

vals = ['a','b','c','d']
cts  = [1,2,3,4]

sz = sum(cts)
spacing = [float(sz)/(ct+1) for ct in cts]
err = [s for s in spacing]
a=[]
for i in range(sz):
    err = [e-1 for e in err]
    m = min(err)
    i = err.index(m)
    a.append(vals[i])
    err[i]+=spacing[i]
print a

yeilds: ['d', 'c', 'b', 'd', 'a', 'c', 'd', 'b', 'c', 'd']

Answer 2

First, try to guess where each letter instance would be, only considering one letter at a time. If there's 10 total, and 3as, try to place the As at index 0, 3, and 7. Calculate these estimated indecies for each letter, and put them in a ordered multiset.

std::multimap<unsigned,char> set;
const unsigned totalcount = ... //for your example this would be 10
for (const auto& letterpair : letters) {
    unsigned lettercount = letterpair.second; //for c this would be 3
    for(unsigned i=0; i<lettercount; ++i) {
        unsigned targetIdx = (2*i*totalcount+1)/lettercount;
        set.insert(std::make_pair(targetIdx, letterpair.first));
    }
}

Then we can simply iterate over the set in order and place each thing in a single index.

std::vector<char> result;
for(const auto& p : set)
    result.push_back(p.second); //insert the letters in order

It's not perfect, but it works pretty darn well considering the speed and simplicity.

For your inputs, it results in bcdadcbdcd: http://coliru.stacked-crooked.com/a/1f83ae4518b7c6ca