题目：
题解：
func removeKdigits(num string, k int) string {stack := []byte{}for i := range num {digit := num[i]for k > 0 && len(stack) > 0 && digit < stack[len(stack)-1] {stack = stack[:len(stack)-1]k--}stack = append(stack, digit)}stack = stack[:len(stack)-k]ans := strings.TrimLeft(string(stack), "0")if ans == "" {ans = "0"}return ans
}
