How to quickly check that all characters are in the window (comparing two maps)?

To quickly check if one map (window) contains all characters from another map, you can compare the keys and their counts. In Go, this can be done as follows:

func containsAll(window, chars map[rune]int) bool {
    for k, v := range chars {
        if window[k] < v {
            return false
        }
    }
    return true
}

Here, window is a map with characters and their counts in the window, chars is a map with characters that must be in the window. The function returns true if, for each character in chars, its count in window is not less.